diff --git a/strbuf.h b/strbuf.h
index 1883494ca3..01c5c6371b 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -205,7 +205,8 @@ extern int strbuf_cmp(const struct strbuf *, const struct strbuf *);
  */
 static inline void strbuf_addch(struct strbuf *sb, int c)
 {
-	strbuf_grow(sb, 1);
+	if (!strbuf_avail(sb))
+		strbuf_grow(sb, 1);
 	sb->buf[sb->len++] = c;
 	sb->buf[sb->len] = '\0';
 }