diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3010,6 +3010,7 @@
     'PhabricatorIteratedMD5PasswordHasherTestCase' => 'infrastructure/util/password/__tests__/PhabricatorIteratedMD5PasswordHasherTestCase.php',
     'PhabricatorIteratorFileUploadSource' => 'applications/files/uploadsource/PhabricatorIteratorFileUploadSource.php',
     'PhabricatorJIRAAuthProvider' => 'applications/auth/provider/PhabricatorJIRAAuthProvider.php',
+    'PhabricatorJSONConfigType' => 'applications/config/type/PhabricatorJSONConfigType.php',
     'PhabricatorJavelinLinter' => 'infrastructure/lint/linter/PhabricatorJavelinLinter.php',
     'PhabricatorJiraIssueHasObjectEdgeType' => 'applications/doorkeeper/edge/PhabricatorJiraIssueHasObjectEdgeType.php',
     'PhabricatorJumpNavHandler' => 'applications/search/engine/PhabricatorJumpNavHandler.php',
@@ -4263,6 +4264,7 @@
     'PhabricatorWebContentSource' => 'infrastructure/contentsource/PhabricatorWebContentSource.php',
     'PhabricatorWebServerSetupCheck' => 'applications/config/check/PhabricatorWebServerSetupCheck.php',
     'PhabricatorWeekStartDaySetting' => 'applications/settings/setting/PhabricatorWeekStartDaySetting.php',
+    'PhabricatorWildConfigType' => 'applications/config/type/PhabricatorWildConfigType.php',
     'PhabricatorWordPressAuthProvider' => 'applications/auth/provider/PhabricatorWordPressAuthProvider.php',
     'PhabricatorWorker' => 'infrastructure/daemon/workers/PhabricatorWorker.php',
     'PhabricatorWorkerActiveTask' => 'infrastructure/daemon/workers/storage/PhabricatorWorkerActiveTask.php',
@@ -8348,6 +8350,7 @@
     'PhabricatorIteratedMD5PasswordHasherTestCase' => 'PhabricatorTestCase',
     'PhabricatorIteratorFileUploadSource' => 'PhabricatorFileUploadSource',
     'PhabricatorJIRAAuthProvider' => 'PhabricatorOAuth1AuthProvider',
+    'PhabricatorJSONConfigType' => 'PhabricatorTextConfigType',
     'PhabricatorJavelinLinter' => 'ArcanistLinter',
     'PhabricatorJiraIssueHasObjectEdgeType' => 'PhabricatorEdgeType',
     'PhabricatorJumpNavHandler' => 'Phobject',
@@ -9839,6 +9842,7 @@
     'PhabricatorWebContentSource' => 'PhabricatorContentSource',
     'PhabricatorWebServerSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorWeekStartDaySetting' => 'PhabricatorSelectSetting',
+    'PhabricatorWildConfigType' => 'PhabricatorJSONConfigType',
     'PhabricatorWordPressAuthProvider' => 'PhabricatorOAuth2AuthProvider',
     'PhabricatorWorker' => 'Phobject',
     'PhabricatorWorkerActiveTask' => 'PhabricatorWorkerTask',
diff --git a/src/applications/config/controller/PhabricatorConfigEditController.php b/src/applications/config/controller/PhabricatorConfigEditController.php
--- a/src/applications/config/controller/PhabricatorConfigEditController.php
+++ b/src/applications/config/controller/PhabricatorConfigEditController.php
@@ -325,40 +325,14 @@
     $e_value = null;
     $errors = array();
 
-
     if ($option->isCustomType()) {
       $info = $option->getCustomObject()->readRequest($option, $request);
       list($e_value, $errors, $set_value, $value) = $info;
     } else {
-      $value = $request->getStr('value');
-      if (!strlen($value)) {
-        $value = null;
-
-        $xaction->setNewValue(
-          array(
-            'deleted' => true,
-            'value'   => null,
-          ));
-
-        return array($e_value, $errors, $value, $xaction);
-      }
-
-      $type = $option->getType();
-      $set_value = null;
-
-      switch ($type) {
-        default:
-          $json = json_decode($value, true);
-          if ($json === null && strtolower($value) != 'null') {
-            $e_value = pht('Invalid');
-            $errors[] = pht(
-              'The given value must be valid JSON. This means, among '.
-              'other things, that you must wrap strings in double-quotes.');
-          } else {
-            $set_value = $json;
-          }
-          break;
-      }
+      throw new Exception(
+        pht(
+          'Unknown configuration option type "%s".',
+          $option->getType()));
     }
 
     if (!$errors) {
@@ -389,13 +363,12 @@
         $option,
         $entry,
         $value);
-    } else {
-      $type = $option->getType();
-      switch ($type) {
-        default:
-          return PhabricatorConfigJSON::prettyPrintJSON($value);
-      }
     }
+
+    throw new Exception(
+      pht(
+        'Unknown configuration option type "%s".',
+        $option->getType()));
   }
 
   private function renderControls(
@@ -417,23 +390,10 @@
         $display_value,
         $e_value);
     } else {
-      $type = $option->getType();
-      switch ($type) {
-        default:
-          $control = id(new AphrontFormTextAreaControl())
-            ->setHeight(AphrontFormTextAreaControl::HEIGHT_VERY_TALL)
-            ->setCustomClass('PhabricatorMonospaced')
-            ->setCaption(pht('Enter value in JSON.'));
-          break;
-      }
-
-      $control
-        ->setLabel(pht('Database Value'))
-        ->setError($e_value)
-        ->setValue($display_value)
-        ->setName('value');
-
-      $controls = array($control);
+      throw new Exception(
+        pht(
+          'Unknown configuration option type "%s".',
+          $option->getType()));
     }
 
     return $controls;
diff --git a/src/applications/config/management/PhabricatorConfigManagementSetWorkflow.php b/src/applications/config/management/PhabricatorConfigManagementSetWorkflow.php
--- a/src/applications/config/management/PhabricatorConfigManagementSetWorkflow.php
+++ b/src/applications/config/management/PhabricatorConfigManagementSetWorkflow.php
@@ -70,6 +70,7 @@
         throw new PhutilArgumentUsageException($ex->getMessage());
       }
     } else {
+      // NOTE: For now, this handles both "wild" values and custom types.
       $type = $option->getType();
       switch ($type) {
         default:
diff --git a/src/applications/config/option/PhabricatorApplicationConfigOptions.php b/src/applications/config/option/PhabricatorApplicationConfigOptions.php
--- a/src/applications/config/option/PhabricatorApplicationConfigOptions.php
+++ b/src/applications/config/option/PhabricatorApplicationConfigOptions.php
@@ -24,6 +24,7 @@
     if ($type) {
       try {
         $type->validateStoredValue($option, $value);
+        $this->didValidateOption($option, $value);
       } catch (PhabricatorConfigValidationException $ex) {
         throw $ex;
       } catch (Exception $ex) {
@@ -32,6 +33,8 @@
         // configuration and raise an error.
         throw new PhabricatorConfigValidationException($ex->getMessage());
       }
+
+      return;
     }
 
     if ($option->isCustomType()) {
@@ -40,12 +43,11 @@
       } catch (Exception $ex) {
         throw new PhabricatorConfigValidationException($ex->getMessage());
       }
-    }
-
-    switch ($option->getType()) {
-      case 'wild':
-      default:
-        break;
+    } else {
+      throw new Exception(
+        pht(
+          'Unknown configuration option type "%s".',
+          $option->getType()));
     }
 
     $this->didValidateOption($option, $value);
diff --git a/src/applications/config/type/PhabricatorJSONConfigType.php b/src/applications/config/type/PhabricatorJSONConfigType.php
new file mode 100644
--- /dev/null
+++ b/src/applications/config/type/PhabricatorJSONConfigType.php
@@ -0,0 +1,38 @@
+<?php
+
+abstract class PhabricatorJSONConfigType
+  extends PhabricatorTextConfigType {
+
+  protected function newCanonicalValue(
+    PhabricatorConfigOption $option,
+    $value) {
+
+    try {
+      $value = phutil_json_decode($value);
+    } catch (Exception $ex) {
+      throw $this->newException(
+        pht(
+          'Value for option "%s" (of type "%s") must be specified in JSON, '.
+          'but input could not be decoded: %s',
+          $option->getKey(),
+          $this->getTypeKey(),
+          $ex->getMessage()));
+    }
+
+    return $value;
+  }
+
+  protected function newControl(PhabricatorConfigOption $option) {
+    return id(new AphrontFormTextAreaControl())
+      ->setHeight(AphrontFormTextAreaControl::HEIGHT_VERY_TALL)
+      ->setCustomClass('PhabricatorMonospaced')
+      ->setCaption(pht('Enter value in JSON.'));
+  }
+
+  public function newDisplayValue(
+    PhabricatorConfigOption $option,
+    $value) {
+    return PhabricatorConfigJSON::prettyPrintJSON($value);
+  }
+
+}
diff --git a/src/applications/config/type/PhabricatorWildConfigType.php b/src/applications/config/type/PhabricatorWildConfigType.php
new file mode 100644
--- /dev/null
+++ b/src/applications/config/type/PhabricatorWildConfigType.php
@@ -0,0 +1,39 @@
+<?php
+
+final class PhabricatorWildConfigType
+  extends PhabricatorJSONConfigType {
+
+  const TYPEKEY = 'wild';
+
+  protected function newCanonicalValue(
+    PhabricatorConfigOption $option,
+    $value) {
+
+    $raw_value = $value;
+
+    // NOTE: We're significantly more liberal about canonicalizing "wild"
+    // values than "JSON" values because they're used to deal with some
+    // unusual edge cases, including situations where old config has been left
+    // in the database and we aren't sure what type it's supposed to be.
+    // Accept anything we can decode.
+
+    $value = json_decode($raw_value, true);
+    if ($value === null && $raw_value != 'null') {
+      throw $this->newException(
+        pht(
+          'Value for option "%s" (of type "%s") must be specified in JSON, '.
+          'but input could not be decoded. (Did you forget to quote a string?)',
+          $option->getKey(),
+          $this->getTypeKey()));
+    }
+
+    return $value;
+  }
+
+  public function validateStoredValue(
+    PhabricatorConfigOption $option,
+    $value) {
+    return;
+  }
+
+}
diff --git a/src/applications/people/config/PhabricatorUserConfigOptions.php b/src/applications/people/config/PhabricatorUserConfigOptions.php
--- a/src/applications/people/config/PhabricatorUserConfigOptions.php
+++ b/src/applications/people/config/PhabricatorUserConfigOptions.php
@@ -43,7 +43,7 @@
       $this->newOption('user.fields', $custom_field_type, $default)
         ->setCustomData(id(new PhabricatorUser())->getCustomFieldBaseClass())
         ->setDescription(pht('Select and reorder user profile fields.')),
-      $this->newOption('user.custom-field-definitions', 'map', array())
+      $this->newOption('user.custom-field-definitions', 'wild', array())
         ->setDescription(pht('Add new simple fields to user profiles.')),
       $this->newOption('user.require-real-name', 'bool', true)
         ->setDescription(pht('Always require real name for user profiles.'))