diff --git a/lib/wind/punycode.c b/lib/wind/punycode.c
index ccd79beb8..0e4544520 100644
--- a/lib/wind/punycode.c
+++ b/lib/wind/punycode.c
@@ -77,7 +77,8 @@ adapt(unsigned delta, unsigned numpoints, int first)
  *
  * @param in an UCS4 string to convert
  * @param in_len the length of in.
- * @param out the resulting puny-coded string.
+ * @param out the resulting puny-coded string. The string is not NUL
+ * terminatied.
  * @param out_len before processing out_len should be the length of
  * the out variable, after processing it will be the length of the out
  * string.
@@ -107,19 +108,24 @@ wind_punycode_label_toascii(const uint32_t *in, size_t in_len,
 	    out[o++] = in[i];
 	}
     }
+    if (o == i) {
+	*out_len = o;
+	return 0;
+    }
     b = h;
     if (b > 0) {
 	if (o >= *out_len)
 	    return WIND_ERR_OVERRUN;
 	out[o++] = 0x2D;
     }
-    while (h < in_len) {
-	if (o + 4 >= *out_len)
-	    return WIND_ERR_OVERRUN;
-	memmove(out + 4, out, o);
-	memcpy(out, "xn--", 4);
-	o += 4;
 
+    if (o + 4 >= *out_len)
+	return WIND_ERR_OVERRUN;
+    memmove(out + 4, out, o);
+    memcpy(out, "xn--", 4);
+    o += 4;
+
+    while (h < in_len) {
 	m = (unsigned)-1;
 	for (i = 0; i < in_len; ++i)
 	    if(in[i] < m && in[i] >= n)