diff --git a/wpiformat/wpiformat/includeorder.py b/wpiformat/wpiformat/includeorder.py
index 2204df7..cf8fd41 100644
--- a/wpiformat/wpiformat/includeorder.py
+++ b/wpiformat/wpiformat/includeorder.py
@@ -228,10 +228,10 @@ def header_sort(self, config_file, lines_list, file_name, start, end,
 
         i = start
         while i < end:
-            if "#ifdef" in lines_list[i]:
+            if "#ifdef" in lines_list[i] or "#ifndef" in lines_list[i]:
                 ifdef_count = 1
                 for j in range(i + 1, end):
-                    if "#ifdef" in lines_list[j]:
+                    if "#ifdef" in lines_list[j] or "#ifndef" in lines_list[j]:
                         ifdef_count += 1
                     elif "#endif" in lines_list[j]:
                         ifdef_count -= 1
@@ -371,6 +371,7 @@ def run_pipeline(self, config_file, name, lines):
         # Write lines from beginning of file to headers
         i = 0
         while i < len(lines_list) and ("#ifdef" not in lines_list[i] and
+                                       "#ifndef" not in lines_list[i] and
                                        "#include" not in lines_list[i]):
             i += 1
         output_list = lines_list[0:i]
diff --git a/wpiformat/wpiformat/test/test_includeorder.py b/wpiformat/wpiformat/test/test_includeorder.py
index f0e80e1..f18016f 100644
--- a/wpiformat/wpiformat/test/test_includeorder.py
+++ b/wpiformat/wpiformat/test/test_includeorder.py
@@ -546,4 +546,50 @@ def test_includeorder():
         "#endif" + os.linesep)
     test.add_latest_input_as_output(True)
 
+    # Ensure #ifndef is handled properly
+    test.add_input("./Test.h",
+        "#ifndef __APPLE__" + os.linesep + \
+        "#include <util.h>" + os.linesep + \
+        "#elif !defined(_WIN32)" + os.linesep + \
+        "#include <pty.h>" + os.linesep + \
+        "#endif" + os.linesep)
+    test.add_latest_input_as_output(True)
+
+    # Ensure #ifndef is handled properly
+    test.add_input("./Test.h",
+        "#ifndef _WIN32" + os.linesep + \
+        "#include <pty.h>" + os.linesep + \
+        "#endif" + os.linesep)
+    test.add_latest_input_as_output(True)
+
+    # Ensure include guards are handled properly
+    test.add_input("./Test.h",
+        "#ifndef CSCORE_CONFIGURABLESOURCEIMPL_H_" + os.linesep + \
+        "#define CSCORE_CONFIGURABLESOURCEIMPL_H_" + os.linesep + \
+        os.linesep + \
+        "#include <atomic>" + os.linesep + \
+        "#include <functional>" + os.linesep + \
+        "#include <memory>" + os.linesep + \
+        "#include <string>" + os.linesep + \
+        "#include <string_view>" + os.linesep + \
+        "#include <vector>" + os.linesep + \
+        os.linesep + \
+        "#include <wpi/span.h>" + os.linesep + \
+        os.linesep + \
+        "#include \"SourceImpl.h\"" + os.linesep + \
+        os.linesep + \
+        "namespace cs {" + os.linesep + \
+        os.linesep + \
+        "class ConfigurableSourceImpl : public SourceImpl {" + os.linesep + \
+        " protected:" + os.linesep + \
+        "  ConfigurableSourceImpl(std::string_view name, wpi::Logger& logger," + os.linesep + \
+        "                         Notifier& notifier, Telemetry& telemetry," + os.linesep + \
+        "                         const VideoMode& mode);" + os.linesep + \
+        "};" + os.linesep + \
+        os.linesep + \
+        "}  // namespace cs" + os.linesep + \
+        os.linesep + \
+        "#endif  // CSCORE_CONFIGURABLESOURCEIMPL_H_" + os.linesep)
+    test.add_latest_input_as_output(True)
+
     test.run(OutputType.FILE)