diff --git a/include/fast_float/constexpr_feature_detect.h b/include/fast_float/constexpr_feature_detect.h
index 3568edf..19c4924 100644
--- a/include/fast_float/constexpr_feature_detect.h
+++ b/include/fast_float/constexpr_feature_detect.h
@@ -115,8 +115,8 @@
 
 #ifdef FASTFLOAT_ASSUME
 // Use the provided definition.
-// #elif FASTFLOAT_HAS_CPP_ATTRIBUTE(assume)
-// #define FASTFLOAT_ASSUME(expr) [[assume(expr)]]
+#elif FASTFLOAT_HAS_CPP_ATTRIBUTE(assume) && !defined(__GNUC__)
+#define FASTFLOAT_ASSUME(expr) [[assume(expr)]]
 #else
 #define FASTFLOAT_ASSUME(expr)
 #endif