diff --git a/src/mem.c b/src/mem.c
index 3aa1be8bb688518ae52e83a84a7d3637e9a1dc81..e6dd3da66b49edf6691bfe96a51e86433d6709cd 100644
--- a/src/mem.c
+++ b/src/mem.c
@@ -396,7 +396,7 @@ void *rt_realloc(void *rmem, rt_size_t newsize)
 
 	/* expand memory */
 	nmem = rt_malloc(newsize);
-	rt_memcpy(nmem, rmem, size);
+	rt_memcpy(nmem, rmem, size < newsize ? size : newsize);
 
 	rt_free(rmem);