diff --git a/Source/NSISO8601DateFormatter.m b/Source/NSISO8601DateFormatter.m
index 6d51afec6f..5d711e92c7 100644
--- a/Source/NSISO8601DateFormatter.m
+++ b/Source/NSISO8601DateFormatter.m
@@ -122,7 +122,7 @@ - (NSString *) _buildFormatWithOptions
     {
       if (_formatOptions & NSISO8601DateFormatWithColonSeparatorInTimeZone)
         {
-          result = [result stringByAppendingString: @"ZZ:ZZ"];
+          result = [result stringByAppendingString: @"ZZZZZ"];
         }
       else
         {