diff --git a/lib/xcodeproj/constants.rb b/lib/xcodeproj/constants.rb
index <HASH>..<HASH> 100644
--- a/lib/xcodeproj/constants.rb
+++ b/lib/xcodeproj/constants.rb
@@ -272,6 +272,6 @@ module Xcodeproj
 
     # @return [Hash] The extensions which are associated with header files.
     #
-    HEADER_FILES_EXTENSIONS = %w(.h .hh .hpp .ipp .H).freeze
+    HEADER_FILES_EXTENSIONS = %w(.h .hh .hpp .ipp).freeze
   end
 end
diff --git a/lib/xcodeproj/project/object/native_target.rb b/lib/xcodeproj/project/object/native_target.rb
index <HASH>..<HASH> 100644
--- a/lib/xcodeproj/project/object/native_target.rb
+++ b/lib/xcodeproj/project/object/native_target.rb
@@ -412,7 +412,7 @@ module Xcodeproj
 
             extension = File.extname(file.path)
             header_extensions = Constants::HEADER_FILES_EXTENSIONS
-            if header_extensions.include?(extension)
+            if header_extensions.include?(extension.downcase)
               headers_build_phase.files << build_file
             else
               if compiler_flags && !compiler_flags.empty?
use case insensitive extension comparison to mark files as headers