diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -397,7 +397,7 @@
     'rsrc/js/application/files/behavior-icon-composer.js' => '38a6cedb',
     'rsrc/js/application/files/behavior-launch-icon-composer.js' => 'a17b84f1',
     'rsrc/js/application/harbormaster/behavior-harbormaster-log.js' => 'b347a301',
-    'rsrc/js/application/herald/HeraldRuleEditor.js' => '27daef73',
+    'rsrc/js/application/herald/HeraldRuleEditor.js' => '2633bef7',
     'rsrc/js/application/herald/PathTypeahead.js' => 'ad486db3',
     'rsrc/js/application/herald/herald-rule-editor.js' => '0922e81d',
     'rsrc/js/application/maniphest/behavior-batch-selector.js' => '139ef688',
@@ -571,7 +571,7 @@
     'global-drag-and-drop-css' => '1d2713a4',
     'harbormaster-css' => '8dfe16b2',
     'herald-css' => '648d39e2',
-    'herald-rule-editor' => '27daef73',
+    'herald-rule-editor' => '2633bef7',
     'herald-test-css' => 'e004176f',
     'inline-comment-summary-css' => '81eb368d',
     'javelin-aphlict' => '022516b4',
@@ -1117,7 +1117,7 @@
       'javelin-json',
       'phabricator-draggable-list',
     ),
-    '27daef73' => array(
+    '2633bef7' => array(
       'multirow-row-manager',
       'javelin-install',
       'javelin-util',
diff --git a/src/applications/harbormaster/herald/HarbormasterRunBuildPlansHeraldAction.php b/src/applications/harbormaster/herald/HarbormasterRunBuildPlansHeraldAction.php
--- a/src/applications/harbormaster/herald/HarbormasterRunBuildPlansHeraldAction.php
+++ b/src/applications/harbormaster/herald/HarbormasterRunBuildPlansHeraldAction.php
@@ -96,4 +96,8 @@
     return $record->getTarget();
   }
 
+  public function isActionAvailable() {
+    return id(new PhabricatorHarbormasterApplication())->isInstalled();
+  }
+
 }
diff --git a/src/applications/herald/action/HeraldAction.php b/src/applications/herald/action/HeraldAction.php
--- a/src/applications/herald/action/HeraldAction.php
+++ b/src/applications/herald/action/HeraldAction.php
@@ -405,4 +405,8 @@
     return array();
   }
 
+  public function isActionAvailable() {
+    return true;
+  }
+
 }
diff --git a/src/applications/herald/adapter/HeraldAdapter.php b/src/applications/herald/adapter/HeraldAdapter.php
--- a/src/applications/herald/adapter/HeraldAdapter.php
+++ b/src/applications/herald/adapter/HeraldAdapter.php
@@ -373,6 +373,16 @@
     return $field->getFieldGroupKey();
   }
 
+  public function isFieldAvailable($field_key) {
+    $field = $this->getFieldImplementation($field_key);
+
+    if (!$field) {
+      return null;
+    }
+
+    return $field->isFieldAvailable();
+  }
+
 
 /* -(  Conditions  )--------------------------------------------------------- */
 
@@ -765,6 +775,16 @@
     return $action->getActionGroupKey();
   }
 
+  public function isActionAvailable($action_key) {
+    $action = $this->getActionImplementation($action_key);
+
+    if (!$action) {
+      return null;
+    }
+
+    return $action->isActionAvailable();
+  }
+
   public function getActions($rule_type) {
     $actions = array();
     foreach ($this->getActionsForRuleType($rule_type) as $key => $action) {
diff --git a/src/applications/herald/controller/HeraldRuleController.php b/src/applications/herald/controller/HeraldRuleController.php
--- a/src/applications/herald/controller/HeraldRuleController.php
+++ b/src/applications/herald/controller/HeraldRuleController.php
@@ -684,7 +684,10 @@
     $group_map = array();
     foreach ($field_map as $field_key => $field_name) {
       $group_key = $adapter->getFieldGroupKey($field_key);
-      $group_map[$group_key][$field_key] = $field_name;
+      $group_map[$group_key][$field_key] = array(
+        'name' => $field_name,
+        'available' => $adapter->isFieldAvailable($field_key),
+      );
     }
 
     return $this->getGroups(
@@ -696,7 +699,10 @@
     $group_map = array();
     foreach ($action_map as $action_key => $action_name) {
       $group_key = $adapter->getActionGroupKey($action_key);
-      $group_map[$group_key][$action_key] = $action_name;
+      $group_map[$group_key][$action_key] = array(
+        'name' => $action_name,
+        'available' => $adapter->isActionAvailable($action_key),
+      );
     }
 
     return $this->getGroups(
diff --git a/src/applications/herald/field/HeraldField.php b/src/applications/herald/field/HeraldField.php
--- a/src/applications/herald/field/HeraldField.php
+++ b/src/applications/herald/field/HeraldField.php
@@ -241,4 +241,8 @@
     return false;
   }
 
+  public function isFieldAvailable() {
+    return true;
+  }
+
 }
diff --git a/src/applications/legalpad/herald/LegalpadRequireSignatureHeraldAction.php b/src/applications/legalpad/herald/LegalpadRequireSignatureHeraldAction.php
--- a/src/applications/legalpad/herald/LegalpadRequireSignatureHeraldAction.php
+++ b/src/applications/legalpad/herald/LegalpadRequireSignatureHeraldAction.php
@@ -130,4 +130,9 @@
       'Require document signatures: %s.',
       $this->renderHandleList($value));
   }
+
+  public function isActionAvailable() {
+    return id(new PhabricatorLegalpadApplication())->isInstalled();
+  }
+
 }
diff --git a/webroot/rsrc/js/application/herald/HeraldRuleEditor.js b/webroot/rsrc/js/application/herald/HeraldRuleEditor.js
--- a/webroot/rsrc/js/application/herald/HeraldRuleEditor.js
+++ b/webroot/rsrc/js/application/herald/HeraldRuleEditor.js
@@ -350,8 +350,10 @@
         sigil: 'field-select'
       };
 
-      var field_select = this._renderGroupSelect(groups, attrs);
-      field_select.value = this._config.conditions[row_id][0];
+      var field_select = this._renderGroupSelect(
+        groups,
+        attrs,
+        this._config.conditions[row_id][0]);
 
       var field_cell = JX.$N('td', {sigil: 'field-cell'}, field_select);
 
@@ -367,18 +369,38 @@
       }
     },
 
-    _renderGroupSelect: function(groups, attrs) {
+    _renderGroupSelect: function(groups, attrs, value) {
       var optgroups = [];
       for (var ii = 0; ii < groups.length; ii++) {
         var group = groups[ii];
         var options = [];
         for (var k in group.options) {
-          options.push(JX.$N('option', {value: k}, group.options[k]));
+          var option = group.options[k];
+
+          var name = option.name;
+          var available = option.available;
+
+          // See T7961. If the option is not marked as "available", we only
+          // include it in the dropdown if the dropdown already has it as a
+          // value. We want to hide options provided by applications which are
+          // not installed, but do not want to break existing rules.
+
+          if (available || (k === value)) {
+            options.push(JX.$N('option', {value: k}, name));
+          }
         }
-        optgroups.push(JX.$N('optgroup', {label: group.label}, options));
+        if (options.length) {
+          optgroups.push(JX.$N('optgroup', {label: group.label}, options));
+        }
+      }
+
+      var select = JX.$N('select', attrs, optgroups);
+
+      if (value !== undefined) {
+        select.value = value;
       }
 
-      return JX.$N('select', attrs, optgroups);
+      return select;
     },
 
     _newAction : function(data) {
@@ -402,8 +424,10 @@
         sigil: 'action-select'
       };
 
-      var action_select = this._renderGroupSelect(groups, attrs);
-      action_select.value = action[0];
+      var action_select = this._renderGroupSelect(
+        groups,
+        attrs,
+        action[0]);
 
       var action_cell = JX.$N('td', {sigil: 'action-cell'}, action_select);