diff --git a/extensions/tags/js/admin/dist/extension.js b/extensions/tags/js/admin/dist/extension.js
index d08445a7a..dee1b7b5b 100644
--- a/extensions/tags/js/admin/dist/extension.js
+++ b/extensions/tags/js/admin/dist/extension.js
@@ -1301,6 +1301,7 @@ System.register('flarum/tags/models/Tag', ['flarum/Model', 'flarum/utils/mixin',
 
         isRestricted: Model.attribute('isRestricted'),
         canStartDiscussion: Model.attribute('canStartDiscussion'),
+        canAddToDiscussion: Model.attribute('canAddToDiscussion'),
 
         isPrimary: computed('position', 'parent', function (position, parent) {
           return position !== null && parent === false;
diff --git a/extensions/tags/js/forum/dist/extension.js b/extensions/tags/js/forum/dist/extension.js
index 68ad9f0c6..131863585 100644
--- a/extensions/tags/js/forum/dist/extension.js
+++ b/extensions/tags/js/forum/dist/extension.js
@@ -446,9 +446,19 @@ System.register('flarum/tags/components/TagDiscussionModal', ['flarum/components
 
             babelHelpers.get(Object.getPrototypeOf(TagDiscussionModal.prototype), 'init', this).call(this);
 
-            this.tags = sortTags(app.store.all('tags').filter(function (tag) {
-              return tag.canStartDiscussion();
-            }));
+            this.tags = app.store.all('tags');
+
+            if (this.props.discussion) {
+              this.tags = this.tags.filter(function (tag) {
+                return tag.canAddToDiscussion() || _this2.props.discussion.tags().indexOf(tag) !== -1;
+              });
+            } else {
+              this.tags = this.tags.filter(function (tag) {
+                return tag.canStartDiscussion();
+              });
+            }
+
+            this.tags = sortTags(this.tags);
 
             this.selected = [];
             this.filter = m.prop('');
@@ -1258,6 +1268,7 @@ System.register('flarum/tags/models/Tag', ['flarum/Model', 'flarum/utils/mixin',
 
         isRestricted: Model.attribute('isRestricted'),
         canStartDiscussion: Model.attribute('canStartDiscussion'),
+        canAddToDiscussion: Model.attribute('canAddToDiscussion'),
 
         isPrimary: computed('position', 'parent', function (position, parent) {
           return position !== null && parent === false;
diff --git a/extensions/tags/js/forum/src/components/TagDiscussionModal.js b/extensions/tags/js/forum/src/components/TagDiscussionModal.js
index 28b7038b3..f81948e8e 100644
--- a/extensions/tags/js/forum/src/components/TagDiscussionModal.js
+++ b/extensions/tags/js/forum/src/components/TagDiscussionModal.js
@@ -14,7 +14,15 @@ export default class TagDiscussionModal extends Modal {
   init() {
     super.init();
 
-    this.tags = sortTags(app.store.all('tags').filter(tag => tag.canStartDiscussion()));
+    this.tags = app.store.all('tags');
+
+    if (this.props.discussion) {
+      this.tags = this.tags.filter(tag => tag.canAddToDiscussion() || this.props.discussion.tags().indexOf(tag) !== -1);
+    } else {
+      this.tags = this.tags.filter(tag => tag.canStartDiscussion());
+    }
+
+    this.tags = sortTags(this.tags);
 
     this.selected = [];
     this.filter = m.prop('');
diff --git a/extensions/tags/js/lib/models/Tag.js b/extensions/tags/js/lib/models/Tag.js
index 04cda1519..b66c1f494 100644
--- a/extensions/tags/js/lib/models/Tag.js
+++ b/extensions/tags/js/lib/models/Tag.js
@@ -23,6 +23,7 @@ export default class Tag extends mixin(Model, {
 
   isRestricted: Model.attribute('isRestricted'),
   canStartDiscussion: Model.attribute('canStartDiscussion'),
+  canAddToDiscussion: Model.attribute('canAddToDiscussion'),
 
   isPrimary: computed('position', 'parent', (position, parent) => position !== null && parent === false)
 }) {}
diff --git a/extensions/tags/src/Access/TagPolicy.php b/extensions/tags/src/Access/TagPolicy.php
index c64ba2a93..49ad05abd 100755
--- a/extensions/tags/src/Access/TagPolicy.php
+++ b/extensions/tags/src/Access/TagPolicy.php
@@ -43,4 +43,14 @@ class TagPolicy extends AbstractPolicy
             return true;
         }
     }
+
+    /**
+     * @param User $actor
+     * @param Tag $tag
+     * @return bool|null
+     */
+    public function addToDiscussion(User $actor, Tag $tag)
+    {
+        return $this->startDiscussion($actor, $tag);
+    }
 }
diff --git a/extensions/tags/src/Api/Serializer/TagSerializer.php b/extensions/tags/src/Api/Serializer/TagSerializer.php
index 256dd4d91..8979456b1 100644
--- a/extensions/tags/src/Api/Serializer/TagSerializer.php
+++ b/extensions/tags/src/Api/Serializer/TagSerializer.php
@@ -40,7 +40,8 @@ class TagSerializer extends AbstractSerializer
             'isChild'            => (bool) $tag->parent_id,
             'isHidden'           => (bool) $tag->is_hidden,
             'lastTime'           => $this->formatDate($tag->last_time),
-            'canStartDiscussion' => $this->actor->can('startDiscussion', $tag)
+            'canStartDiscussion' => $this->actor->can('startDiscussion', $tag),
+            'canAddToDiscussion' => $this->actor->can('addToDiscussion', $tag)
         ];
 
         if ($this->actor->isAdmin()) {
diff --git a/extensions/tags/src/Listener/SaveTagsToDatabase.php b/extensions/tags/src/Listener/SaveTagsToDatabase.php
index 30a4b0b4a..8454a09a6 100755
--- a/extensions/tags/src/Listener/SaveTagsToDatabase.php
+++ b/extensions/tags/src/Listener/SaveTagsToDatabase.php
@@ -81,12 +81,18 @@ class SaveTagsToDatabase
 
             if ($discussion->exists) {
                 $oldTags = $discussion->tags()->get();
-                $oldTagIds = $oldTags->lists('id');
+                $oldTagIds = $oldTags->lists('id')->all();
 
                 if ($oldTagIds == $newTagIds) {
                     return;
                 }
 
+                foreach ($newTags as $tag) {
+                    if (! in_array($tag->id, $oldTagIds) && $actor->cannot('addToDiscussion', $tag)) {
+                        throw new PermissionDeniedException;
+                    }
+                }
+                
                 $discussion->raise(
                     new DiscussionWasTagged($discussion, $actor, $oldTags->all())
                 );