diff --git a/racket/src/racket/include/scheme.h b/racket/src/racket/include/scheme.h
index ad5d29be16..ec54c190a2 100644
--- a/racket/src/racket/include/scheme.h
+++ b/racket/src/racket/include/scheme.h
@@ -253,23 +253,23 @@ extern "C"
 #endif
 
 #if !defined(MZ_NORETURN)
-#if defined(__GNUC__) || defined(__clang__)
-#define MZ_NORETURN __attribute__((noreturn))
-#elif defined(_MSC_VER)
-#define MZ_NORETURN __declspec(noreturn)
-#else
-#define MZ_NORETURN
-#endif /* defined(__GNUC__) || defined(__clang__) */
+# if defined(__GNUC__) || defined(__clang__)
+#  define MZ_NORETURN __attribute__((noreturn))
+# elif defined(_MSC_VER)
+#  define MZ_NORETURN __declspec(noreturn)
+# else
+#  define MZ_NORETURN
+# endif /* defined(__GNUC__) || defined(__clang__) */
 #endif /* !defined(MZ_NORETURN) */
 
 #if !defined(MZ_UNREACHABLE)
-#if defined(__GNUC__) || defined(__clang__)
-#define MZ_UNREACHABLE __builtin_unreachable()
-#elif defined(_MSC_VER)
-#define MZ_UNREACHABLE __assume(0)
-#else
-#define MZ_UNREACHABLE
-#endif /* defined(__GNUC__) || defined(__clang__) */
+# if (defined(__GNUC__) && (__GNUC__ > 4)) || defined(__clang__)
+#  define MZ_UNREACHABLE __builtin_unreachable()
+# elif defined(_MSC_VER)
+#  define MZ_UNREACHABLE __assume(0)
+# else
+#  define MZ_UNREACHABLE
+# endif /* defined(__GNUC__) || defined(__clang__) */
 #endif /* !defined(MZ_UNREACHABLE) */
 
 /* Allowed by all configurations, currently: */