diff --git a/Modules/CMakeCCompilerId.c.in b/Modules/CMakeCCompilerId.c.in
index 30ad9824ee..0cb8724fb8 100644
--- a/Modules/CMakeCCompilerId.c.in
+++ b/Modules/CMakeCCompilerId.c.in
@@ -61,7 +61,7 @@ const char* info_language_standard_default =
 
 const char* info_language_extensions_default = "INFO" ":" "extensions_default["
 /* !defined(_MSC_VER) to exclude Clang's MSVC compatibility mode. */
-#if (defined(__clang__) || defined(__GNUC__) ||                               \
+#if (defined(__clang__) || defined(__GNUC__) || defined(__xlC__) ||           \
      defined(__TI_COMPILER_VERSION__)) &&                                     \
   !defined(__STRICT_ANSI__) && !defined(_MSC_VER)
   "ON"
diff --git a/Modules/CMakeCXXCompilerId.cpp.in b/Modules/CMakeCXXCompilerId.cpp.in
index e7a5487426..4904249add 100644
--- a/Modules/CMakeCXXCompilerId.cpp.in
+++ b/Modules/CMakeCXXCompilerId.cpp.in
@@ -67,7 +67,7 @@ const char* info_language_standard_default = "INFO" ":" "standard_default["
 
 const char* info_language_extensions_default = "INFO" ":" "extensions_default["
 /* !defined(_MSC_VER) to exclude Clang's MSVC compatibility mode. */
-#if (defined(__clang__) || defined(__GNUC__) ||                               \
+#if (defined(__clang__) || defined(__GNUC__) || defined(__xlC__) ||           \
      defined(__TI_COMPILER_VERSION__)) &&                                     \
   !defined(__STRICT_ANSI__) && !defined(_MSC_VER)
   "ON"