diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 533f301ae..96c7e6c6d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1844,7 +1844,8 @@ static void mbedtls_ssl_cf_memcpy_if_eq( unsigned char *dst,
 #endif
 
     /* dst[i] = c1 != c2 ? dst[i] : src[i] */
-    for( size_t i = 0; i < len; i++ )
+    size_t i;
+    for( i = 0; i < len; i++ )
         dst[i] = ( dst[i] & mask ) | ( src[i] & ~mask );
 }