diff --git a/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php b/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php
--- a/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php
+++ b/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php
@@ -179,6 +179,10 @@
         $type->getEditType());
 
       $value_type = $type->getValueType();
+      if (!strlen($value_type)) {
+        $value_type = '?';
+      }
+
       $value_description = $type->getValueDescription();
 
       $table = array();
diff --git a/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditField.php b/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditField.php
--- a/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditField.php
+++ b/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditField.php
@@ -36,8 +36,15 @@
   }
 
   protected function newEditType() {
-    return id(new PhabricatorCustomFieldEditType())
+    $type = id(new PhabricatorCustomFieldEditType())
       ->setCustomField($this->getCustomField());
+
+    $http_type = $this->getHTTPParameterType();
+    if ($http_type) {
+      $type->setValueType($http_type->getTypeName());
+    }
+
+    return $type;
   }
 
   public function getValueForTransaction() {
@@ -65,8 +72,13 @@
   }
 
   public function getConduitEditTypes() {
-    // TODO: For now, don't support custom fields over Conduit.
-    return array();
+    $field = $this->getCustomField();
+
+    if (!$field->shouldAppearInConduitTransactions()) {
+      return array();
+    }
+
+    return parent::getConduitEditTypes();
   }
 
   protected function newHTTPParameterType() {
diff --git a/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditType.php b/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditType.php
--- a/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditType.php
+++ b/src/infrastructure/customfield/editor/PhabricatorCustomFieldEditType.php
@@ -4,6 +4,7 @@
   extends PhabricatorEditType {
 
   private $customField;
+  private $valueType;
 
   public function setCustomField(PhabricatorCustomField $custom_field) {
     $this->customField = $custom_field;
@@ -14,9 +15,13 @@
     return $this->customField;
   }
 
+  public function setValueType($value_type) {
+    $this->valueType = $value_type;
+    return $this;
+  }
+
   public function getValueType() {
-    // TODO: Improve.
-    return 'custom';
+    return $this->valueType;
   }
 
   public function getMetadata() {
diff --git a/src/infrastructure/customfield/field/PhabricatorCustomField.php b/src/infrastructure/customfield/field/PhabricatorCustomField.php
--- a/src/infrastructure/customfield/field/PhabricatorCustomField.php
+++ b/src/infrastructure/customfield/field/PhabricatorCustomField.php
@@ -1323,6 +1323,14 @@
   }
 
 
+  public function shouldAppearInConduitTransactions() {
+    if ($this->proxy) {
+      return $this->proxy->shouldAppearInConduitDictionary();
+    }
+    return false;
+  }
+
+
 /* -(  Herald  )------------------------------------------------------------- */
 
 
diff --git a/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php b/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php
--- a/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php
+++ b/src/infrastructure/customfield/standard/PhabricatorStandardCustomField.php
@@ -433,4 +433,8 @@
       ->setEditTypeKey($short);
   }
 
+  public function shouldAppearInConduitTransactions() {
+    return true;
+  }
+
 }
diff --git a/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldDate.php b/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldDate.php
--- a/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldDate.php
+++ b/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldDate.php
@@ -191,4 +191,10 @@
     }
   }
 
+  public function shouldAppearInConduitTransactions() {
+    // TODO: Dates are complicated and we don't yet support handling them from
+    // Conduit.
+    return false;
+  }
+
 }