diff --git a/m4/check-libc.m4 b/m4/check-libc.m4
index a8f6646..f2eb3eb 100644
--- a/m4/check-libc.m4
+++ b/m4/check-libc.m4
@@ -59,7 +59,7 @@ AM_CONDITIONAL([HAVE_TIMINGSAFE_MEMCMP], [test "x$ac_cv_func_timingsafe_memcmp"
 
 # Override arc4random_buf implementations with known issues
 AM_CONDITIONAL([HAVE_ARC4RANDOM_BUF],
-	[test "x$USE_BUILTIN_ARC4RANDOM" != yes \
+	[test "x$USE_BUILTIN_ARC4RANDOM" != xyes \
 	   -a "x$ac_cv_func_arc4random_buf" = xyes])
 
 # Check for getentropy fallback dependencies