diff --git a/src/stdio/vasprintf.c b/src/stdio/vasprintf.c
index 08251bc2..d55fe32f 100644
--- a/src/stdio/vasprintf.c
+++ b/src/stdio/vasprintf.c
@@ -5,11 +5,16 @@
 
 int vasprintf(char **s, const char *fmt, va_list ap)
 {
-	va_list ap2;
-	va_copy(ap2, ap);
-	int l = vsnprintf(0, 0, fmt, ap2);
-	va_end(ap2);
+	size_t l;
+	*s = 0;
+	FILE *f = open_memstream(s, &l);
+	if (!f)
+		return -1;
 
-	if (l<0 || !(*s=malloc(l+1U))) return -1;
-	return vsnprintf(*s, l+1U, fmt, ap);
+	if ((l = vfprintf(f, fmt, ap)) == -1) {
+		free(*s);
+		*s = 0;
+	}
+	fclose(f);
+	return l;
 }