diff --git a/lib/include_/bitutil.h b/lib/include_/bitutil.h
index 53990d3..f5664bd 100644
--- a/lib/include_/bitutil.h
+++ b/lib/include_/bitutil.h
@@ -145,7 +145,14 @@ void bitzdec(unsigned char *in, unsigned n,                     unsigned esize);
 
 //------- Lossy floating point transform: pad the trailing mantissa bits with zeros according to the error e (ex. e=0.00001)
 // must include float.h to use _Float16 (see icapp.c)
- #if defined(FLT16_MAX) 
+#if defined(__clang__) && defined(__is_identifier)
+  #if !__is_identifier(_Float16)
+    #undef FLT16_BUILTIN
+  #endif
+#elif defined(FLT16_MAX)
+#define FLT16_BUILTIN
+#endif
+ #ifdef FLT16_BUILTIN
 _Float16 _fprazor16(_Float16 d, float e, int lg2e);  
 void fprazor16(_Float16 *in, unsigned n, _Float16  *out, float  e);
   #endif