diff --git a/CRM/Core/BAO/CustomField.php b/CRM/Core/BAO/CustomField.php
index 8d232803944e..1dc707ecd688 100644
--- a/CRM/Core/BAO/CustomField.php
+++ b/CRM/Core/BAO/CustomField.php
@@ -2156,7 +2156,7 @@ public static function fixOptionGroups($customFieldId, $optionGroupId) {
     );
     // get the updated option group
     // if both are same return
-    if ($currentOptionGroupId == $optionGroupId) {
+    if (!$currentOptionGroupId || $currentOptionGroupId == $optionGroupId) {
       return;
     }
 
diff --git a/tests/phpunit/api/v3/CustomFieldTest.php b/tests/phpunit/api/v3/CustomFieldTest.php
index 6e822b1bf11a..6b6573e82826 100644
--- a/tests/phpunit/api/v3/CustomFieldTest.php
+++ b/tests/phpunit/api/v3/CustomFieldTest.php
@@ -300,6 +300,28 @@ public function testCustomFieldExistingOptionGroup() {
     $this->assertEquals($optionGroupID, 3);
   }
 
+  /**
+   * Test adding an optionGroup to an existing field doesn't cause a fatal error.
+   *
+   * (this was happening due to a check running despite no existing option_group_id)
+   */
+  public function testUpdateCustomFieldAddOptionGroup() {
+    $customGroup = $this->customGroupCreate(['extends' => 'Organization', 'title' => 'test_group']);
+    $params = [
+      'custom_group_id' => $customGroup['id'],
+      'label' => 'Organization Gender',
+      'html_type' => 'Text',
+      'data_type' => 'Int',
+    ];
+
+    $customField = $this->callAPISuccess('custom_field', 'create', $params);
+    $this->callAPISuccess('CustomField', 'create', [
+      'option_group_id' => 3,
+      'id' => $customField['id'],
+      'html_type' => 'Select',
+    ]);
+  }
+
   /**
    * Test custom field get works & return param works
    */