diff --git a/GTG/gtk/browser/modify_tags.py b/GTG/gtk/browser/modify_tags.py
index 2a3cf2f16c..d307d54bdd 100644
--- a/GTG/gtk/browser/modify_tags.py
+++ b/GTG/gtk/browser/modify_tags.py
@@ -47,6 +47,27 @@ def __init__(self, tag_completion, app):
         self.last_tag_entry = _("NewTag")
         self.last_apply_to_subtasks = False
 
+
+    def parse_tag_list(self, text):
+        """ Parse a line of a list of tasks. User can specify if the tag is
+        positive or not by prepending '!'.
+
+        @param  text:  string entry from user
+        @return: list of tupples (tag, is_positive)
+        """
+
+        result = []
+        for tag in text.split():
+            if tag.startswith('!'):
+                tag = tag[1:]
+                is_positive = False
+            else:
+                is_positive = True
+
+            result.append((tag, is_positive))
+        return result
+
+
     def modify_tags(self, tasks):
         """ Show and run dialog for selected tasks """
 
@@ -71,7 +92,7 @@ def on_response(self, widget, response):
     def apply_changes(self):
         """ Apply changes """
 
-        tags = parse_tag_list(self._tag_entry.get_text())
+        tags = self.parse_tag_list(self._tag_entry.get_text())
 
         # If the checkbox is checked, find all subtasks
         if self._apply_to_subtasks_check.get_active():