diff --git a/src/lib/libast/features/mmap b/src/lib/libast/features/mmap
index 2ed3405d3..eedca7da2 100644
--- a/src/lib/libast/features/mmap
+++ b/src/lib/libast/features/mmap
@@ -219,12 +219,13 @@ tst	mmap_devzero note{ use mmap on /dev/zero to get raw memory }end execute{
 	}
 }end
 
-tst	note{ mmap is worth using }end output{
+tst	note{ mmap is fast enough to be worth using }end output{
 	#if !_lib_mmap
 	(
 	#endif
 	#include <unistd.h>
 	#include <fcntl.h>
+	#include <string.h>
 	#include <sys/types.h>
 	#include <sys/mman.h>
 	#include <sys/stat.h>