diff --git a/includes/webform.report.inc b/includes/webform.report.inc
index d72d087..4f3726b 100644
--- a/includes/webform.report.inc
+++ b/includes/webform.report.inc
@@ -1634,6 +1634,8 @@ function webform_results_get_extra_data(array $submissions) {
       $extra_data[$submission->sid] = array();
     }
   }
+
+  // Only invoke the hook when data of unknown submissions are requested.
   if ($unknown) {
     // array_merge_recursive makes impossible for hook implementations to return
     // data keyed by submission id.
@@ -1645,7 +1647,13 @@ function webform_results_get_extra_data(array $submissions) {
     }
   }
 
-  return $extra_data;
+  // Only return extra data for submission ids requested.
+  $return_data = array();
+  foreach ($submissions as $submission) {
+    $return_data[$submission->sid] = $extra_data[$submission->sid];
+  }
+
+  return $return_data;
 }
 
 /**