diff --git a/Source/cmGeneratorExpressionEvaluator.cxx b/Source/cmGeneratorExpressionEvaluator.cxx
index 34d44340d..c1d108681 100644
--- a/Source/cmGeneratorExpressionEvaluator.cxx
+++ b/Source/cmGeneratorExpressionEvaluator.cxx
@@ -201,6 +201,8 @@ static const struct LowerCaseNode : public cmGeneratorExpressionNode
 {
   LowerCaseNode() {}
 
+  bool AcceptsArbitraryContentParameter() const { return true; }
+
   std::string Evaluate(const std::vector<std::string> &parameters,
                        cmGeneratorExpressionContext *,
                        const GeneratorExpressionContent *,
@@ -215,6 +217,8 @@ static const struct UpperCaseNode : public cmGeneratorExpressionNode
 {
   UpperCaseNode() {}
 
+  bool AcceptsArbitraryContentParameter() const { return true; }
+
   std::string Evaluate(const std::vector<std::string> &parameters,
                        cmGeneratorExpressionContext *,
                        const GeneratorExpressionContent *,
@@ -229,6 +233,8 @@ static const struct MakeCIdentifierNode : public cmGeneratorExpressionNode
 {
   MakeCIdentifierNode() {}
 
+  bool AcceptsArbitraryContentParameter() const { return true; }
+
   std::string Evaluate(const std::vector<std::string> &parameters,
                        cmGeneratorExpressionContext *,
                        const GeneratorExpressionContent *,
diff --git a/Tests/GeneratorExpression/CMakeLists.txt b/Tests/GeneratorExpression/CMakeLists.txt
index edadb87ee..892f80fd6 100644
--- a/Tests/GeneratorExpression/CMakeLists.txt
+++ b/Tests/GeneratorExpression/CMakeLists.txt
@@ -193,9 +193,9 @@ add_custom_target(check-part3 ALL
     -Dtest_platform_id_Linux=$<PLATFORM_ID:Linux>
     -Dtest_platform_id_Windows=$<PLATFORM_ID:Windows>
     -Dtest_platform_id_Darwin=$<PLATFORM_ID:Darwin>
-    -Dlower_case=$<LOWER_CASE:MiXeD>
-    -Dupper_case=$<UPPER_CASE:MiXeD>
-    -Dmake_c_identifier=$<MAKE_C_IDENTIFIER:4foo:+bar-$>
+    -Dlower_case=$<LOWER_CASE:Mi,XeD>
+    -Dupper_case=$<UPPER_CASE:MiX,eD>
+    -Dmake_c_identifier=$<MAKE_C_IDENTIFIER:4f,oo:+bar-$>
     -P ${CMAKE_CURRENT_SOURCE_DIR}/check-part3.cmake
   COMMAND ${CMAKE_COMMAND} -E echo "check done (part 3 of 3)"
   VERBATIM
diff --git a/Tests/GeneratorExpression/check-part3.cmake b/Tests/GeneratorExpression/check-part3.cmake
index a86db313c..3361eebd0 100644
--- a/Tests/GeneratorExpression/check-part3.cmake
+++ b/Tests/GeneratorExpression/check-part3.cmake
@@ -34,6 +34,6 @@ foreach(system Linux Windows Darwin)
     check(test_platform_id_${system} 0)
   endif()
 endforeach()
-check(lower_case "mixed")
-check(upper_case "MIXED")
-check(make_c_identifier "_4foo__bar__")
+check(lower_case "mi,xed")
+check(upper_case "MIX,ED")
+check(make_c_identifier "_4f_oo__bar__")