diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 756360b18..8d3ab61ef 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -600,9 +600,9 @@ void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
 static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
 {
     size_t i;
-    const unsigned char *A = (const unsigned char *) a;
-    const unsigned char *B = (const unsigned char *) b;
-    unsigned char diff = 0;
+    volatile const unsigned char *A = (volatile const unsigned char *) a;
+    volatile const unsigned char *B = (volatile const unsigned char *) b;
+    volatile unsigned char diff = 0;
 
     for( i = 0; i < n; i++ )
         diff |= A[i] ^ B[i];