diff --git a/src/string.c b/src/string.c
index ad11d54..49fdc9b 100644
--- a/src/string.c
+++ b/src/string.c
@@ -19,7 +19,7 @@ Str str_slice(Str str, U32 start, U32 len)
 Str str_concat(Allocator *alloc, Str first, Str second)
 {
     Str str;
-
+    Assert(first.len <= U32_Max - second.len);
     str.len = first.len + second.len;
     str.str = allocator_push(alloc, str.len, 1);;