diff --git a/gsl/gsl_assert b/gsl/gsl_assert
index 34b3ecb..6d8760d 100644
--- a/gsl/gsl_assert
+++ b/gsl/gsl_assert
@@ -39,11 +39,11 @@
 #define GSL_STRINGIFY(x) GSL_STRINGIFY_DETAIL(x)
 
 #if defined(__clang__) || defined(__GNUC__)
-#define GSL_LIKELY(x)    __builtin_expect (!!(x), 1)
-#define GSL_UNLIKELY(x)  __builtin_expect (!!(x), 0)
+#define GSL_LIKELY(x) __builtin_expect (!!(x), 1)
+#define GSL_UNLIKELY(x) __builtin_expect (!!(x), 0)
 #else
-#define GSL_LIKELY(x)
-#define GSL_UNLIKELY(x)
+#define GSL_LIKELY(x) (x)
+#define GSL_UNLIKELY(x) (x)
 #endif
 
 //