diff --git a/src/applications/conduit/parametertype/ConduitParameterType.php b/src/applications/conduit/parametertype/ConduitParameterType.php
--- a/src/applications/conduit/parametertype/ConduitParameterType.php
+++ b/src/applications/conduit/parametertype/ConduitParameterType.php
@@ -38,6 +38,9 @@
     return $this->getParameterValue($request, $key);
   }
 
+  final public function getKeys($key) {
+    return $this->getParameterKeys($key);
+  }
 
   final public function getDefaultValue() {
     return $this->getParameterDefault();
@@ -86,6 +89,10 @@
     return $request[$key];
   }
 
+  protected function getParameterKeys($key) {
+    return array($key);
+  }
+
   abstract protected function getParameterTypeName();
 
 
diff --git a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
--- a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
+++ b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
@@ -1094,6 +1094,22 @@
       }
     }
 
+    $valid_constraints = array();
+    foreach ($fields as $field) {
+      foreach ($field->getValidConstraintKeys() as $key) {
+        $valid_constraints[$key] = true;
+      }
+    }
+
+    foreach ($constraints as $key => $constraint) {
+      if (empty($valid_constraints[$key])) {
+        throw new Exception(
+          pht(
+            'Constraint "%s" is not a valid constraint for this query.',
+            $key));
+      }
+    }
+
     foreach ($fields as $field) {
       if (!$field->getValueExistsInConduitRequest($constraints)) {
         continue;
diff --git a/src/applications/search/field/PhabricatorSearchField.php b/src/applications/search/field/PhabricatorSearchField.php
--- a/src/applications/search/field/PhabricatorSearchField.php
+++ b/src/applications/search/field/PhabricatorSearchField.php
@@ -329,6 +329,11 @@
       $this->getConduitKey());
   }
 
+  public function getValidConstraintKeys() {
+    return $this->getConduitParameterType()->getKeys(
+      $this->getConduitKey());
+  }
+
 
 /* -(  Utility Methods )----------------------------------------------------- */