diff --git a/openmp/runtime/src/kmp_os.h b/openmp/runtime/src/kmp_os.h
--- a/openmp/runtime/src/kmp_os.h
+++ b/openmp/runtime/src/kmp_os.h
@@ -300,6 +300,7 @@
 // case label is intentional and should not be diagnosed by a compiler
 //   Code from libcxx/include/__config
 // Use a function like macro to imply that it must be followed by a semicolon
+#if !KMP_COMPILER_GCC || __GNUC__ >= 5
 #if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
 #  define KMP_FALLTHROUGH() [[fallthrough]]
 #elif __has_cpp_attribute(clang::fallthrough)
@@ -309,6 +310,9 @@
 #else
 #  define KMP_FALLTHROUGH() ((void)0)
 #endif
+#else // !KMP_COMPILER_GCC || __GNUC__ >= 5
+#define KMP_FALLTHROUGH() ((void)0)
+#endif // !KMP_COMPILER_GCC || __GNUC__ >= 5
 
 // Define attribute that indicates a function does not return
 #if __cplusplus >= 201103L