diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 006c0477215eb..c6e1776656047 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -2137,7 +2137,7 @@ Parser::parseAttributeArguments(SourceLoc attrLoc, StringRef attrName,
   }
 
   return parseList(tok::r_paren, parensRange.Start, parensRange.End,
-                   /*allow sep after last*/ true,
+                   /*AllowSepAfterLast=*/true,
                    {diag::attr_expected_rparen, {attrName, isModifier}},
                    parseArg);
 }
@@ -3243,7 +3243,8 @@ ParserStatus Parser::parseNewDeclAttribute(DeclAttributes &Attributes,
     StringRef AttrName = "@_originallyDefinedIn";
     bool SuppressLaterDiags = false;
     bool ParsedUnrecognizedPlatformName = false;
-    if (parseList(tok::r_paren, LeftLoc, RightLoc, false,
+    if (parseList(tok::r_paren, LeftLoc, RightLoc,
+                  /*AllowSepAfterLast=*/false,
                   diag::originally_defined_in_missing_rparen,
                   [&]() -> ParserStatus {
       SWIFT_DEFER {
@@ -4976,7 +4977,7 @@ ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc) {
   SourceLoc rParenLoc;
   bool foundParamId = false;
   status = parseList(
-      tok::r_paren, lParenLoc, rParenLoc, /*AllowSepAfterLast*/ false,
+      tok::r_paren, lParenLoc, rParenLoc, /*AllowSepAfterLast=*/false,
       diag::expected_rparen_after_lifetime_dependence, [&]() -> ParserStatus {
         ParserStatus listStatus;
         foundParamId = true;
@@ -9525,6 +9526,11 @@ ParserStatus Parser::parsePrimaryAssociatedTypeList(
 
     // Parse the comma, if the list continues.
     HasNextParam = consumeIf(tok::comma);
+    
+    // The list ends if we find a trailing comma
+    if (startsWithGreater(Tok)) {
+      break;
+    }
   } while (HasNextParam);
 
   return Result;
diff --git a/lib/Parse/ParseType.cpp b/lib/Parse/ParseType.cpp
index 18cfad4d45e5e..a66aed29cc3cd 100644
--- a/lib/Parse/ParseType.cpp
+++ b/lib/Parse/ParseType.cpp
@@ -742,6 +742,10 @@ ParserStatus Parser::parseGenericArguments(SmallVectorImpl<TypeRepr *> &Args,
       // Parse the comma, if the list continues.
       if (!consumeIf(tok::comma))
         break;
+      
+      // If the comma was a trailing comma, finish parsing the list of types
+      if (startsWithGreater(Tok))
+        break;
     }
   }
 
@@ -1161,7 +1165,7 @@ ParserResult<TypeRepr> Parser::parseTypeTupleBody() {
   SmallVector<TupleTypeReprElement, 8> ElementsR;
 
   ParserStatus Status = parseList(tok::r_paren, LPLoc, RPLoc,
-                                  /*AllowSepAfterLast=*/false,
+                                  /*AllowSepAfterLast=*/true,
                                   diag::expected_rparen_tuple_type_list,
                                   [&] () -> ParserStatus {
     TupleTypeReprElement element;
@@ -1605,7 +1609,8 @@ bool Parser::canParseGenericArguments() {
     if (!canParseType())
       return false;
     // Parse the comma, if the list continues.
-  } while (consumeIf(tok::comma));
+    // This could be the trailing comma.
+  } while (consumeIf(tok::comma) && !startsWithGreater(Tok));
 
   if (!startsWithGreater(Tok)) {
     return false;
diff --git a/test/Casting/ParameterizedExistentials.swift b/test/Casting/ParameterizedExistentials.swift
index ea893d7c02912..c6fd92d30c49f 100644
--- a/test/Casting/ParameterizedExistentials.swift
+++ b/test/Casting/ParameterizedExistentials.swift
@@ -46,7 +46,10 @@ struct GenericHolder<T>: Holder {
   init(value: T) { self.value = value}
 }
 
-protocol PairType<T, U> {
+protocol PairType<
+  T,
+  U,
+> {
   associatedtype T
   associatedtype U
 
diff --git a/test/Parse/trailing-comma.swift b/test/Parse/trailing-comma.swift
index 200733e8885e1..453c3388f9eaa 100644
--- a/test/Parse/trailing-comma.swift
+++ b/test/Parse/trailing-comma.swift
@@ -9,6 +9,10 @@ let values: [Int,] = [] // expected-note {{to match this opening '['}} expected-
 // Tuple and Tuple Pattern
 
 let _ = (a: 1, b: 2, c: 3,)
+let _: (a: Int, b: Int, c: Int,) = (a: 1, b: 2, c: 3,)
+
+// Closures
+let _: (String, Int, Float,) -> Void
 
 let (_, _,) = (0,1,)
 
@@ -34,7 +38,7 @@ struct S<T1, T2,> { }
 
 func foo<T1, T2,>() { }
 
-protocol P<T1, T2> {
+protocol P<T1, T2,> {
     associatedtype T1
     associatedtype T2
 }
@@ -98,7 +102,7 @@ struct Foo {
 
 }
 
-func f(in: @differentiable(reverse,) (Int) -> Int) { } // expected-warning {{@differentiable' has been renamed to '@differentiable(reverse)' and will be removed in the next release}} expected-error {{unexpected ',' separator}} expected-error {{expected ',' separator}} expected-error {{unnamed parameters must be written with the empty name '_'}} 
+func f(in: @differentiable(reverse,) (Int) -> Int) { } // expected-warning {{@differentiable' has been renamed to '@differentiable(reverse)' and will be removed in the next release}} expected-error {{expected ',' separator}} expected-error {{unnamed parameters must be written with the empty name '_'}}
 
 @derivative(of: Self.other,) // expected-error {{unexpected ',' separator}}
 func foo() {}
@@ -135,4 +139,12 @@ if true, { } // expected-error {{expected '{' after 'if' condition}}
 
 guard true, else { } // expected-error {{expected expression in conditional}} 
 
-while true, { } // expected-error {{expected '{' after 'while' condition}} 
\ No newline at end of file
+while true, { } // expected-error {{expected '{' after 'while' condition}} 
+
+if #available(OSX 51,) { // expected-error {{expected platform name}}
+}
+
+@available(OSX 10.7, iOS 7.0, *,) // expected-error {{expected platform name}} expected-error {{expected declaration}}
+@_originallyDefinedIn(module: "HighLevel", OSX 10.9, iOS 13.0,) // expected-error {{unexpected ',' separator}}
+@backDeployed(before: OSX 10.9,) // expected-error {{unexpected ',' separator}}
+public struct StructWithAvailability {}
diff --git a/test/decl/ext/typealias.swift b/test/decl/ext/typealias.swift
index c5917a0a0d565..3d33655f7a80b 100644
--- a/test/decl/ext/typealias.swift
+++ b/test/decl/ext/typealias.swift
@@ -78,3 +78,16 @@ extension FooIntBarFloatDoubleInner {
   }
 }
 
+struct Foo2<T1, T2, T3,> {}
+
+typealias Bar2<
+  T1,
+  T2,
+> = Foo2<
+  T1,
+  T2,
+  Bool,
+>
+
+let _ = Foo2<Int, Bool, String,>.self
+let _ = Bar2<Int, Bool,>()
diff --git a/test/type/types.swift b/test/type/types.swift
index 09b217c147875..7176d1298c0f5 100644
--- a/test/type/types.swift
+++ b/test/type/types.swift
@@ -219,3 +219,18 @@ do {
     subscript(_: inout Double...) -> Bool { true } // expected-error {{'inout' may only be used on function or initializer parameters}}
   }
 }
+
+let tupleTypeWithTrailingComma: (
+  bar: String,
+  quux: String,
+)
+
+let _ = (bar: String, quux: String,).self
+
+let closureTypeWithTrailingCommas: (
+  String,
+  String,
+) -> (
+  bar: String,
+  quux: String,
+)