diff --git a/src/gmutil.c b/src/gmutil.c

index c0eda099..cca930cc 100644

--- a/src/gmutil.c

+++ b/src/gmutil.c

@@ -290,7 +290,8 @@ const iString *absoluteUrl_String(const iString *d, const iString *urlMaybeRelat

 appendCStr_String(absolute, "://");

 /* Authority. */ {

     const iUrl *selHost = isDef_(rel.host) ? &rel : &orig;

- const iBool isIPv6 = iStrStrN(selHost->host.start, ":", size_Range(&selHost->host)) != NULL;

+ const iBool isIPv6 = size_Range(&selHost->host) > 0 &&

+ iStrStrN(selHost->host.start, ":", size_Range(&selHost->host)) != NULL;

     iString *decHost = punyDecodeHost_(selHost->host);

     if (isIPv6) {

         appendCStr_String(absolute, "[");