diff --git a/app/core/gimptag.c b/app/core/gimptag.c
index 8d0639aa59..2682169362 100644
--- a/app/core/gimptag.c
+++ b/app/core/gimptag.c
@@ -246,7 +246,7 @@ gimp_tag_compare_func (const void *p1,
 /**
  * gimp_tag_compare_with_string:
  * @tag:        a #GimpTag object.
- * @tag_string: pointer to right-hand #GimpTag object.
+ * @tag_string: the string to compare to.
  *
  * Compares tag and a string according to tag comparison rules. Similar to
  * gimp_tag_compare_func(), but can be used without creating temporary tag
@@ -276,6 +276,42 @@ gimp_tag_compare_with_string (GimpTag     *tag,
   return result;
 }
 
+/**
+ * gimp_tag_has_prefix:
+ * @tag:           a #GimpTag object.
+ * @prefix_string: the prefix to compare to.
+ *
+ * Compares tag and a prefix according to tag comparison rules. Similar to
+ * gimp_tag_compare_with_string(), but does not work on the collate key
+ * because that can't be matched partially.
+ *
+ * Return value: wheher #tag starts with @prefix_string.
+ **/
+gboolean
+gimp_tag_has_prefix (GimpTag     *tag,
+                     const gchar *prefix_string)
+{
+  gchar    *case_folded1;
+  gchar    *case_folded2;
+  gboolean  has_prefix;
+
+  g_return_val_if_fail (GIMP_IS_TAG (tag), FALSE);
+  g_return_val_if_fail (prefix_string != NULL, FALSE);
+
+  case_folded1 = g_utf8_casefold (g_quark_to_string (tag->tag), -1);
+  case_folded2 = g_utf8_casefold (prefix_string, -1);
+
+  has_prefix = g_str_has_prefix (case_folded1, case_folded2);
+
+  g_free (case_folded1);
+  g_free (case_folded2);
+
+  g_printerr ("'%s' has prefix '%s': %d\n",
+              g_quark_to_string (tag->tag), prefix_string, has_prefix);
+
+  return has_prefix;
+}
+
 /**
  * gimp_tag_string_make_valid:
  * @tag_string: a text string.
diff --git a/app/core/gimptag.h b/app/core/gimptag.h
index fc168f1d06..af564823ef 100644
--- a/app/core/gimptag.h
+++ b/app/core/gimptag.h
@@ -68,6 +68,8 @@ gint          gimp_tag_compare_func        (const void     *p1,
                                             const void     *p2);
 gint          gimp_tag_compare_with_string (GimpTag        *tag,
                                             const gchar    *tag_string);
+gboolean      gimp_tag_has_prefix          (GimpTag        *tag,
+                                            const gchar    *prefix_string);
 gchar       * gimp_tag_string_make_valid   (const gchar    *tag_string);
 gboolean      gimp_tag_is_tag_separator    (gunichar        c);
 
diff --git a/app/widgets/gimptagentry.c b/app/widgets/gimptagentry.c
index 2e9bc5b2fe..3e38447622 100644
--- a/app/widgets/gimptagentry.c
+++ b/app/widgets/gimptagentry.c
@@ -1044,13 +1044,11 @@ gimp_tag_entry_get_completion_candidates (GimpTagEntry  *tag_entry,
                                           gchar        **used_tags,
                                           gchar         *src_prefix)
 {
-  GList       *candidates = NULL;
-  GList       *all_tags;
-  GList       *list;
-  const gchar *tag_name;
-  gint         i;
-  gint         length;
-  gchar       *prefix;
+  GList *candidates = NULL;
+  GList *all_tags;
+  GList *list;
+  gint   length;
+  gchar *prefix;
 
   if (! src_prefix || strlen (src_prefix) < 1)
     return NULL;
@@ -1066,10 +1064,10 @@ gimp_tag_entry_get_completion_candidates (GimpTagEntry  *tag_entry,
     {
       GimpTag *tag = list->data;
 
-      tag_name = gimp_tag_get_name (tag);
-
-      if (g_str_has_prefix (tag_name, prefix))
+      if (gimp_tag_has_prefix (tag, prefix))
         {
+          gint i;
+
           /* check if tag is not already entered */
           for (i = 0; i < length; i++)
             {
diff --git a/app/widgets/gimptagpopup.c b/app/widgets/gimptagpopup.c
index a00789aeb0..738e86153c 100644
--- a/app/widgets/gimptagpopup.c
+++ b/app/widgets/gimptagpopup.c
@@ -210,12 +210,10 @@ gimp_tag_popup_constructed (GObject *object)
   GList               *tag_list;
   GList               *tag_iterator;
   gint                 i;
-  gint                 j;
   gint                 max_height;
   gint                 screen_height;
   gchar              **current_tags;
   gint                 current_count;
-  const gchar         *list_tag;
   GdkRectangle         popup_rects[2]; /* variants of popup placement */
   GdkRectangle         popup_rect; /* best popup rect in screen coordinates */
 
@@ -255,15 +253,14 @@ gimp_tag_popup_constructed (GObject *object)
        i++, tag_iterator = g_list_next (tag_iterator))
     {
       PopupTagData *tag_data = &popup->tag_data[i];
+      gint          j;
 
       tag_data->tag   = tag_iterator->data;
       tag_data->state = GTK_STATE_NORMAL;
 
-      list_tag = gimp_tag_get_name (tag_data->tag);
-
       for (j = 0; j < current_count; j++)
         {
-          if (! strcmp (current_tags[j], list_tag))
+          if (! gimp_tag_compare_with_string (tag_data->tag, current_tags[j]))
             {
               tag_data->state = GTK_STATE_SELECTED;
               break;
@@ -966,12 +963,11 @@ static void
 gimp_tag_popup_toggle_tag (GimpTagPopup *popup,
                            PopupTagData *tag_data)
 {
-  gchar       **current_tags;
-  GString      *tag_str;
-  const gchar  *tag;
-  gint          length;
-  gint          i;
-  gboolean      tag_toggled_off = FALSE;
+  gchar    **current_tags;
+  GString   *tag_str;
+  gint       length;
+  gint       i;
+  gboolean   tag_toggled_off = FALSE;
 
   if (tag_data->state == GTK_STATE_NORMAL)
     {
@@ -986,13 +982,12 @@ gimp_tag_popup_toggle_tag (GimpTagPopup *popup,
       return;
     }
 
-  tag = gimp_tag_get_name (tag_data->tag);
   current_tags = gimp_tag_entry_parse_tags (GIMP_TAG_ENTRY (popup->combo_entry));
   tag_str = g_string_new ("");
   length = g_strv_length (current_tags);
   for (i = 0; i < length; i++)
     {
-      if (! strcmp (current_tags[i], tag))
+      if (! gimp_tag_compare_with_string (tag_data->tag, current_tags[i]))
         {
           tag_toggled_off = TRUE;
         }
@@ -1018,7 +1013,7 @@ gimp_tag_popup_toggle_tag (GimpTagPopup *popup,
           g_string_append_c (tag_str, ' ');
         }
 
-      g_string_append (tag_str, tag);
+      g_string_append (tag_str, gimp_tag_get_name (tag_data->tag));
     }
 
   gimp_tag_entry_set_tag_string (GIMP_TAG_ENTRY (popup->combo_entry),