diff --git a/lib/vtls/darwinssl.c b/lib/vtls/darwinssl.c
index 6f9c6012e..18751ca49 100644
--- a/lib/vtls/darwinssl.c
+++ b/lib/vtls/darwinssl.c
@@ -1797,7 +1797,7 @@ static int read_cert(const char *file, unsigned char **out, size_t *outlen)
 {
   int fd;
   ssize_t n, len = 0, cap = 512;
-  unsigned char buf[cap], *data;
+  unsigned char buf[512], *data;
 
   fd = open(file, 0);
   if(fd < 0)