diff --git a/strbuf.c b/strbuf.c
index f4201e160..cbada946c 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -111,12 +111,13 @@ void strbuf_addf(struct strbuf *sb, const char *fmt, ...)
 	int len;
 	va_list ap;
 
+	if (!strbuf_avail(sb))
+		strbuf_grow(sb, 64);
 	va_start(ap, fmt);
 	len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
 	va_end(ap);
-	if (len < 0) {
-		len = 0;
-	}
+	if (len < 0)
+		die("your vsnprintf is broken");
 	if (len > strbuf_avail(sb)) {
 		strbuf_grow(sb, len);
 		va_start(ap, fmt);
diff --git a/trace.c b/trace.c
index 69fa05e64..0d89dbe77 100644
--- a/trace.c
+++ b/trace.c
@@ -72,7 +72,7 @@ void trace_printf(const char *fmt, ...)
 	if (!fd)
 		return;
 
-	strbuf_init(&buf, 0);
+	strbuf_init(&buf, 64);
 	va_start(ap, fmt);
 	len = vsnprintf(buf.buf, strbuf_avail(&buf), fmt, ap);
 	va_end(ap);
@@ -103,7 +103,7 @@ void trace_argv_printf(const char **argv, int count, const char *fmt, ...)
 	if (!fd)
 		return;
 
-	strbuf_init(&buf, 0);
+	strbuf_init(&buf, 64);
 	va_start(ap, fmt);
 	len = vsnprintf(buf.buf, strbuf_avail(&buf), fmt, ap);
 	va_end(ap);