diff --git a/git-compat-util.h b/git-compat-util.h
index 02a73ee..fe845ae 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -388,6 +388,8 @@
 
 static inline size_t xsize_t(off_t len)
 {
+	if (len > (size_t) len)
+		die("Cannot handle files this big");
 	return (size_t)len;
 }