diff --git a/strbuf.h b/strbuf.h
index 07060ce893..9e6d9fa53f 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -3,8 +3,6 @@
 
 /* See Documentation/technical/api-strbuf.txt */
 
-#include <assert.h>
-
 extern char strbuf_slopbuf[];
 struct strbuf {
 	size_t alloc;
@@ -33,9 +31,8 @@ static inline size_t strbuf_avail(const struct strbuf *sb) {
 extern void strbuf_grow(struct strbuf *, size_t);
 
 static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
-	if (!sb->alloc)
-		strbuf_grow(sb, 0);
-	assert(len < sb->alloc);
+	if (len > (sb->alloc ? sb->alloc - 1 : 0))
+		die("BUG: strbuf_setlen() beyond buffer");
 	sb->len = len;
 	sb->buf[len] = '\0';
 }