diff --git a/build.sbt b/build.sbt
index 849f3f46..325eb852 100644
--- a/build.sbt
+++ b/build.sbt
@@ -25,9 +25,9 @@ val scalacOpts = dotcOpts ++ List(
   // 57 inferred return type Scala 2.13 cat=scala3-migration
   "-Wconf:msg=inferred:ws",
   // 2 deprecations Scala 2.12 Stack - fixed for 2.13
-  "-Wconf:msg=poorly-performing:ws"
+  "-Wconf:msg=poorly-performing:ws",
   // uncomment to see messages
-  // "-Wconf:any:warning-verbose"
+  "-Wconf:any:warning-verbose"
 )
 
 Compile / console / scalacOptions --= Seq(
diff --git a/sconfig/jvm/src/main/scala/org/ekrich/config/impl/ConfigBeanImpl.scala b/sconfig/jvm/src/main/scala/org/ekrich/config/impl/ConfigBeanImpl.scala
index 58100483..920272eb 100644
--- a/sconfig/jvm/src/main/scala/org/ekrich/config/impl/ConfigBeanImpl.scala
+++ b/sconfig/jvm/src/main/scala/org/ekrich/config/impl/ConfigBeanImpl.scala
@@ -112,7 +112,7 @@ object ConfigBeanImpl {
       if (!problems.isEmpty)
         throw new ConfigException.ValidationFailed(problems)
       // Fill in the bean instance
-      val bean = clazz.getConstructor().newInstance()
+      val bean = clazz.getDeclaredConstructor().newInstance()
       for (beanProp <- beanProps.asScala) {
         breakable {
           val setter = beanProp.getWriteMethod
@@ -137,11 +137,16 @@ object ConfigBeanImpl {
       }
       bean
     } catch {
-      case e: InstantiationException =>
+      case e: NoSuchMethodException =>
         throw new ConfigException.BadBean(
           clazz.getName + " needs a public no-args constructor to be used as a bean",
           e
         )
+      case e: InstantiationException =>
+        throw new ConfigException.BadBean(
+          clazz.getName + " needs to be instantiatable to be used as a bean",
+          e
+        )
       case e: IllegalAccessException =>
         throw new ConfigException.BadBean(
           clazz.getName + " getters and setters are not accessible, they must be for use as a bean",
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/ConfigFactory.scala b/sconfig/shared/src/main/scala/org/ekrich/config/ConfigFactory.scala
index 61061963..be0636ef 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/ConfigFactory.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/ConfigFactory.scala
@@ -1049,14 +1049,27 @@ object ConfigFactory extends PlatformConfigFactory {
     if (className != null) {
       try {
         classOf[ConfigLoadingStrategy].cast(
-          Class.forName(className).getConstructor().newInstance()
+          Class
+            .forName(className)
+            .asSubclass(classOf[ConfigLoadingStrategy])
+            .getDeclaredConstructor()
+            .newInstance()
         )
       } catch {
+        // possibly InvocationTargetException
         case e: Throwable =>
-          throw new ConfigException.BugOrBroken(
-            "Failed to load strategy: " + className,
-            e
-          )
+          val cause = e.getCause()
+          if (cause == null) {
+            throw new ConfigException.BugOrBroken(
+              "Failed to load strategy: " + className,
+              e
+            )
+          } else {
+            throw new ConfigException.BugOrBroken(
+              "Failed to load strategy: " + className,
+              cause
+            )
+          }
       }
     } else {
       new DefaultConfigLoadingStrategy()
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/AbstractConfigObject.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/AbstractConfigObject.scala
index 74c8e9b8..25a1dbf4 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/AbstractConfigObject.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/AbstractConfigObject.scala
@@ -164,7 +164,7 @@ abstract class AbstractConfigObject(_origin: ConfigOrigin)
   override def constructDelayedMerge(
       origin: ConfigOrigin,
       stack: ju.List[AbstractConfigValue]
-  ) =
+  ): AbstractConfigObject =
     new ConfigDelayedMergeObject(origin, stack)
 
   override def mergedWithObject(
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigBoolean.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigBoolean.scala
index 97fcf075..420fa7aa 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigBoolean.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigBoolean.scala
@@ -19,7 +19,8 @@ final class ConfigBoolean(origin: ConfigOrigin, val value: jl.Boolean)
 
   override def transformToString: String = value.toString()
 
-  override def newCopy(origin: ConfigOrigin) = new ConfigBoolean(origin, value)
+  override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
+    new ConfigBoolean(origin, value)
 
   // serialization all goes through SerializedConfigValue (signature is critical)
   @throws[ObjectStreamException]
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigConcatenation.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigConcatenation.scala
index df428600..99c7cd9f 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigConcatenation.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigConcatenation.scala
@@ -144,11 +144,11 @@ final class ConfigConcatenation(
       "need to Config#resolve(), see the API docs for Config#resolve(); substitution not resolved: " + this
     )
 
-  override def valueType = throw notResolved
+  override def valueType: ConfigValueType = throw notResolved
 
-  override def unwrapped = throw notResolved
+  override def unwrapped: AnyRef = throw notResolved
 
-  override def newCopy(newOrigin: ConfigOrigin) =
+  override def newCopy(newOrigin: ConfigOrigin): AbstractConfigValue =
     new ConfigConcatenation(newOrigin, pieces)
 
   override def ignoresFallbacks: Boolean = {
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMerge.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMerge.scala
index f967e56d..9fc5139e 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMerge.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMerge.scala
@@ -10,6 +10,7 @@ import org.ekrich.config.ConfigException
 import org.ekrich.config.ConfigOrigin
 import org.ekrich.config.ConfigRenderOptions
 import org.ekrich.config.impl.AbstractConfigValue._
+import org.ekrich.config.ConfigValueType
 
 /**
  * The issue here is that we want to first merge our stack of config files, and
@@ -227,12 +228,12 @@ final class ConfigDelayedMerge(
       )
   }
 
-  override def valueType =
+  override def valueType: ConfigValueType =
     throw new ConfigException.NotResolved(
       "called valueType() on value with unresolved substitutions, need to Config#resolve() first, see API docs"
     )
 
-  override def unwrapped =
+  override def unwrapped: AnyRef =
     throw new ConfigException.NotResolved(
       "called unwrapped() on value with unresolved substitutions, need to Config#resolve() first, see API docs"
     )
@@ -274,7 +275,7 @@ final class ConfigDelayedMerge(
   override def ignoresFallbacks: Boolean =
     ConfigDelayedMerge.stackIgnoresFallbacks(stack)
 
-  override def newCopy(newOrigin: ConfigOrigin) =
+  override def newCopy(newOrigin: ConfigOrigin): AbstractConfigValue =
     new ConfigDelayedMerge(newOrigin, stack)
 
   override final def mergedWithTheUnmergeable(
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMergeObject.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMergeObject.scala
index b64997fa..a18abc18 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMergeObject.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDelayedMergeObject.scala
@@ -114,19 +114,22 @@ final class ConfigDelayedMergeObject(
       mergeable: ConfigMergeable
   ): ConfigDelayedMergeObject =
     super.withFallback(mergeable).asInstanceOf[ConfigDelayedMergeObject]
-  override def withOnlyKey(key: String) =
+  override def withOnlyKey(key: String): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
-  override def withoutKey(key: String) =
+  override def withoutKey(key: String): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
-  override def withOnlyPathOrNull(path: Path) =
+  override def withOnlyPathOrNull(path: Path): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
-  override def withOnlyPath(path: Path) =
+  override def withOnlyPath(path: Path): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
-  override def withoutPath(path: Path) =
+  override def withoutPath(path: Path): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
-  override def withValue(key: String, value: ConfigValue) =
+  override def withValue(
+      key: String,
+      value: ConfigValue
+  ): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
-  override def withValue(path: Path, value: ConfigValue) =
+  override def withValue(path: Path, value: ConfigValue): AbstractConfigObject =
     throw ConfigDelayedMergeObject.notResolved
   override def unmergedValues: ju.Collection[AbstractConfigValue] = stack
   override def canEqual(other: Any): Boolean =
@@ -158,18 +161,24 @@ final class ConfigDelayedMergeObject(
   ): Unit = {
     render(sb, indent, atRoot, null, options)
   }
-  override def unwrapped = throw ConfigDelayedMergeObject.notResolved
-  override def get(key: Any) = throw ConfigDelayedMergeObject.notResolved
-  override def remove(key: Any) = throw ConfigDelayedMergeObject.notResolved
-  override def containsKey(key: Any) =
+  override def unwrapped: ju.Map[String, AnyRef] =
     throw ConfigDelayedMergeObject.notResolved
-  override def containsValue(value: Any) =
+  override def get(key: Any): AbstractConfigValue =
+    throw ConfigDelayedMergeObject.notResolved
+  override def remove(key: Any): ConfigValue =
+    throw ConfigDelayedMergeObject.notResolved
+  override def containsKey(key: Any): Boolean =
+    throw ConfigDelayedMergeObject.notResolved
+  override def containsValue(value: Any): Boolean =
+    throw ConfigDelayedMergeObject.notResolved
+  override def entrySet: ju.Set[ju.Map.Entry[String, ConfigValue]] =
+    throw ConfigDelayedMergeObject.notResolved
+  override def isEmpty: Boolean = throw ConfigDelayedMergeObject.notResolved
+  override def keySet: ju.Set[String] =
+    throw ConfigDelayedMergeObject.notResolved
+  override def size: Int = throw ConfigDelayedMergeObject.notResolved
+  override def values: ju.Collection[ConfigValue] =
     throw ConfigDelayedMergeObject.notResolved
-  override def entrySet = throw ConfigDelayedMergeObject.notResolved
-  override def isEmpty = throw ConfigDelayedMergeObject.notResolved
-  override def keySet = throw ConfigDelayedMergeObject.notResolved
-  override def size = throw ConfigDelayedMergeObject.notResolved
-  override def values = throw ConfigDelayedMergeObject.notResolved
 
   // exercised in ValidationTest.validationFailedSerializable
   // and ConfigTest.test01Serializable
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDouble.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDouble.scala
index 9905226e..521f1e4c 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDouble.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigDouble.scala
@@ -29,7 +29,7 @@ final class ConfigDouble(
 
   override def doubleValue: Double = value
 
-  override def newCopy(origin: ConfigOrigin) =
+  override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
     new ConfigDouble(origin, value, originalText)
 
   // serialization all goes through SerializedConfigValue
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigInt.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigInt.scala
index 0d45ab37..c325470b 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigInt.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigInt.scala
@@ -29,7 +29,7 @@ final class ConfigInt(
 
   override def doubleValue: Double = value.toDouble
 
-  override def newCopy(origin: ConfigOrigin) =
+  override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
     new ConfigInt(origin, value, originalText)
 
   // serialization all goes through SerializedConfigValue
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigLong.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigLong.scala
index 8b9f4b5a..87339228 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigLong.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigLong.scala
@@ -28,7 +28,7 @@ final class ConfigLong(
 
   override def doubleValue: Double = value.toDouble
 
-  override def newCopy(origin: ConfigOrigin) =
+  override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
     new ConfigLong(origin, value, originalText)
 
   // serialization all goes through SerializedConfigValue
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeArray.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeArray.scala
index 2d259a16..8ecc4cb2 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeArray.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeArray.scala
@@ -5,6 +5,8 @@ import java.{util => ju}
 final class ConfigNodeArray private[impl] (
     children: ju.Collection[AbstractConfigNode]
 ) extends ConfigNodeComplexValue(children) {
-  override def newNode(nodes: ju.Collection[AbstractConfigNode]) =
+  override def newNode(
+      nodes: ju.Collection[AbstractConfigNode]
+  ): ConfigNodeComplexValue =
     new ConfigNodeArray(nodes)
 }
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeConcatenation.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeConcatenation.scala
index 0d4e11f7..55e6341c 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeConcatenation.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeConcatenation.scala
@@ -5,6 +5,8 @@ import java.{util => ju}
 final class ConfigNodeConcatenation private[impl] (
     children: ju.Collection[AbstractConfigNode]
 ) extends ConfigNodeComplexValue(children) {
-  override def newNode(nodes: ju.Collection[AbstractConfigNode]) =
+  override def newNode(
+      nodes: ju.Collection[AbstractConfigNode]
+  ): ConfigNodeComplexValue =
     new ConfigNodeConcatenation(nodes)
 }
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeObject.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeObject.scala
index 1a57855c..34a11f26 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeObject.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeObject.scala
@@ -8,7 +8,9 @@ import scala.util.control.Breaks._
 final class ConfigNodeObject private[impl] (
     _children: ju.Collection[AbstractConfigNode]
 ) extends ConfigNodeComplexValue(_children) {
-  override def newNode(nodes: ju.Collection[AbstractConfigNode]) =
+  override def newNode(
+      nodes: ju.Collection[AbstractConfigNode]
+  ): ConfigNodeComplexValue =
     new ConfigNodeObject(nodes)
 
   def hasValue(desiredPath: Path): Boolean =
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeRoot.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeRoot.scala
index f27ad1af..c5934d71 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeRoot.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNodeRoot.scala
@@ -10,7 +10,9 @@ final class ConfigNodeRoot private[impl] (
     _children: ju.Collection[AbstractConfigNode],
     val origin: ConfigOrigin
 ) extends ConfigNodeComplexValue(_children) {
-  override def newNode(nodes: ju.Collection[AbstractConfigNode]) =
+  override def newNode(
+      nodes: ju.Collection[AbstractConfigNode]
+  ): ConfigNodeComplexValue =
     throw new ConfigException.BugOrBroken("Tried to indent the root object")
 
   private[impl] def value: ConfigNodeComplexValue =
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNull.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNull.scala
index 4b2a90db..a725b2b7 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNull.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigNull.scala
@@ -36,7 +36,8 @@ final class ConfigNull(origin: ConfigOrigin)
     sb.append("null")
   }
 
-  override def newCopy(origin: ConfigOrigin) = new ConfigNull(origin)
+  override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
+    new ConfigNull(origin)
 
   // serialization all goes through SerializedConfigValue
   @throws[ObjectStreamException]
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigReference.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigReference.scala
index 406cc03c..f532e275 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigReference.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigReference.scala
@@ -5,6 +5,7 @@ import java.{util => ju}
 import org.ekrich.config.ConfigException
 import org.ekrich.config.ConfigOrigin
 import org.ekrich.config.ConfigRenderOptions
+import org.ekrich.config.ConfigValueType
 
 /**
  * ConfigReference replaces ConfigReference (the older class kept for back
@@ -24,9 +25,9 @@ final class ConfigReference(
     new ConfigException.NotResolved(
       "need to Config#resolve(), see the API docs for Config#resolve(); substitution not resolved: " + this
     )
-  override def valueType = throw notResolved
-  override def unwrapped = throw notResolved
-  override def newCopy(newOrigin: ConfigOrigin) =
+  override def valueType: ConfigValueType = throw notResolved
+  override def unwrapped: AnyRef = throw notResolved
+  override def newCopy(newOrigin: ConfigOrigin): AbstractConfigValue =
     new ConfigReference(newOrigin, expression, prefixLength)
   override def ignoresFallbacks = false
   override def unmergedValues: ju.Collection[ConfigReference] =
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigString.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigString.scala
index 4f405e5d..a74b2ee2 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigString.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/ConfigString.scala
@@ -16,7 +16,7 @@ object ConfigString {
       origin: ConfigOrigin,
       value: String
   ) extends ConfigString(origin, value) {
-    override def newCopy(origin: ConfigOrigin) =
+    override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
       new ConfigString.Quoted(origin, value)
 
     // serialization all goes through SerializedConfigValue
@@ -36,7 +36,7 @@ object ConfigString {
       origin: ConfigOrigin,
       value: String
   ) extends ConfigString(origin, value) {
-    override def newCopy(origin: ConfigOrigin) =
+    override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
       new ConfigString.Unquoted(origin, value)
 
     @throws[ObjectStreamException]
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/Parseable.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/Parseable.scala
index e3cfbdb7..4d35d540 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/Parseable.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/Parseable.scala
@@ -113,7 +113,9 @@ object Parseable {
   ) extends Parseable(options) {
     postConstruct(options)
     @throws[IOException]
-    override protected def reader() = throw new FileNotFoundException(message)
+    override protected def reader(): Reader = throw new FileNotFoundException(
+      message
+    )
     override protected def createOrigin(): ConfigOrigin =
       SimpleConfigOrigin.newSimple(what)
   }
@@ -184,7 +186,7 @@ object Parseable {
       postConstruct(options)
     }
     @throws[IOException]
-    override protected def reader() =
+    override protected def reader(): Reader =
       throw new ConfigException.BugOrBroken(
         "reader() without options should not be called on ParseableURL"
       )
@@ -341,7 +343,7 @@ object Parseable {
       with Relativizer {
     postConstruct(options)
     @throws[IOException]
-    override protected def reader() =
+    override protected def reader(): Reader =
       throw new ConfigException.BugOrBroken(
         "reader() should not be called on resources"
       )
@@ -445,7 +447,7 @@ object Parseable {
   ) extends Parseable(options) {
     postConstruct(options)
     @throws[IOException]
-    override protected def reader() =
+    override protected def reader(): Reader =
       throw new ConfigException.BugOrBroken(
         "reader() should not be called on props"
       )
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SerializedConfigValue.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SerializedConfigValue.scala
index 36abbe4a..a23e047c 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SerializedConfigValue.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SerializedConfigValue.scala
@@ -27,6 +27,7 @@ import org.ekrich.config.ConfigList
 import org.ekrich.config.ConfigObject
 import org.ekrich.config.ConfigOrigin
 import org.ekrich.config.ConfigValue
+import org.ekrich.config.ConfigValueType
 
 /**
  * Deliberately shoving all the serialization code into this class instead of
@@ -398,9 +399,10 @@ class SerializedConfigValue() // this has to be public for the Java deserializer
     in.readFully(bytes)
     new DataInputStream(new ByteArrayInputStream(bytes))
   }
-  override def valueType = throw SerializedConfigValue.shouldNotBeUsed
-  override def unwrapped = throw SerializedConfigValue.shouldNotBeUsed
-  override def newCopy(origin: ConfigOrigin) =
+  override def valueType: ConfigValueType =
+    throw SerializedConfigValue.shouldNotBeUsed
+  override def unwrapped: AnyRef = throw SerializedConfigValue.shouldNotBeUsed
+  override def newCopy(origin: ConfigOrigin): AbstractConfigValue =
     throw SerializedConfigValue.shouldNotBeUsed
   override final def toString: String =
     getClass.getSimpleName + "(value=" + value + ",wasConfig=" + wasConfig + ")"
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigDocument.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigDocument.scala
index 4a6577aa..421d1deb 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigDocument.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigDocument.scala
@@ -38,7 +38,7 @@ final class SimpleConfigDocument private[impl] (
     options = options.setOriginComments(false)
     withValueText(path, newValue.render(options).trim)
   }
-  override def withoutPath(path: String) =
+  override def withoutPath(path: String): ConfigDocument =
     new SimpleConfigDocument(
       configNodeTree.setValue(path, null, parseOptions.getSyntax),
       parseOptions
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigList.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigList.scala
index a8b11faa..d39c5d5c 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigList.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigList.scala
@@ -269,28 +269,29 @@ final class SimpleConfigList(
   override def toArray: Array[Object] = value.toArray
   override def toArray[T](a: Array[T with Object]): Array[T with Object] =
     value.toArray[T](a)
-  override def add(e: ConfigValue) =
+  override def add(e: ConfigValue): Boolean =
     throw SimpleConfigList.weAreImmutable("add")
   override def add(index: Int, element: ConfigValue): Unit = {
     throw SimpleConfigList.weAreImmutable("add")
   }
-  override def addAll(c: ju.Collection[_ <: ConfigValue]) =
+  override def addAll(c: ju.Collection[_ <: ConfigValue]): Boolean =
     throw SimpleConfigList.weAreImmutable("addAll")
-  override def addAll(index: Int, c: ju.Collection[_ <: ConfigValue]) =
+  override def addAll(index: Int, c: ju.Collection[_ <: ConfigValue]): Boolean =
     throw SimpleConfigList.weAreImmutable("addAll")
   override def clear(): Unit = {
     throw SimpleConfigList.weAreImmutable("clear")
   }
-  override def remove(o: Any) = throw SimpleConfigList.weAreImmutable("remove")
-  override def remove(index: Int) =
+  override def remove(o: Any): Boolean =
     throw SimpleConfigList.weAreImmutable("remove")
-  override def removeAll(c: ju.Collection[_]) =
+  override def remove(index: Int): ConfigValue =
+    throw SimpleConfigList.weAreImmutable("remove")
+  override def removeAll(c: ju.Collection[_]): Boolean =
     throw SimpleConfigList.weAreImmutable("removeAll")
-  override def retainAll(c: ju.Collection[_]) =
+  override def retainAll(c: ju.Collection[_]): Boolean =
     throw SimpleConfigList.weAreImmutable("retainAll")
-  override def set(index: Int, element: ConfigValue) =
+  override def set(index: Int, element: ConfigValue): ConfigValue =
     throw SimpleConfigList.weAreImmutable("set")
-  override def newCopy(newOrigin: ConfigOrigin) =
+  override def newCopy(newOrigin: ConfigOrigin): AbstractConfigValue =
     new SimpleConfigList(newOrigin, value)
   final private[impl] def concatenate(other: SimpleConfigList) = {
     val combinedOrigin = SimpleConfigOrigin.mergeOrigins(origin, other.origin)
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigObject.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigObject.scala
index 18c0750f..f4536b5b 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigObject.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleConfigObject.scala
@@ -593,7 +593,8 @@ final class SimpleConfigObject(
 
   override def size: Int = value.size
 
-  override def values = new ju.HashSet[ConfigValue](value.values)
+  override def values: ju.Collection[ConfigValue] =
+    new ju.HashSet[ConfigValue](value.values)
 
   // serialization all goes through SerializedConfigValue
   @throws[ObjectStreamException]
diff --git a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleIncludeContext.scala b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleIncludeContext.scala
index 12adbd66..423363e1 100644
--- a/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleIncludeContext.scala
+++ b/sconfig/shared/src/main/scala/org/ekrich/config/impl/SimpleIncludeContext.scala
@@ -26,7 +26,9 @@ class SimpleIncludeContext(parseable: Parseable, options: ConfigParseOptions)
 
   override def parseOptions: ConfigParseOptions = options
 
-  override def setParseOptions(options: ConfigParseOptions) =
+  override def setParseOptions(
+      options: ConfigParseOptions
+  ): ConfigIncludeContext =
     new SimpleIncludeContext(
       parseable,
       options.setSyntax(null).setOriginDescription(null)