diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 8d35c9c00..db0299eda 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -5429,7 +5429,7 @@ int mbedtls_ssl_read(mbedtls_ssl_context *ssl, unsigned char *buf, size_t len)
     n = (len < ssl->in_msglen)
         ? len : ssl->in_msglen;
 
-    if (buf) {
+    if (len != 0) {
         memcpy(buf, ssl->in_offt, n);
         ssl->in_msglen -= n;
     }