diff --git a/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php b/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php
index 4417e912b1..7b92da9961 100644
--- a/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php
+++ b/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php
@@ -30,7 +30,7 @@ protected function initializeIterator() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return count($this->getCommentVariables());
   }
 
diff --git a/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php b/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
index a54b17d9d1..452c6bbfde 100644
--- a/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
+++ b/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
@@ -145,7 +145,7 @@ public function getIds() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return $this->initializeIterator()->count();
   }
 
diff --git a/core/modules/file/src/Plugin/migrate/source/d6/UploadInstance.php b/core/modules/file/src/Plugin/migrate/source/d6/UploadInstance.php
index 17c34bf3ab..f4182a927e 100644
--- a/core/modules/file/src/Plugin/migrate/source/d6/UploadInstance.php
+++ b/core/modules/file/src/Plugin/migrate/source/d6/UploadInstance.php
@@ -78,7 +78,7 @@ public function fields() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return count($this->initializeIterator());
   }
 
diff --git a/core/modules/migrate/src/Plugin/migrate/source/DummyQueryTrait.php b/core/modules/migrate/src/Plugin/migrate/source/DummyQueryTrait.php
index b77f95e273..efe56b41fa 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/DummyQueryTrait.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/DummyQueryTrait.php
@@ -27,7 +27,7 @@ public function query() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return 1;
   }
 
diff --git a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
index 429a1457a8..e34c4adfde 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -436,7 +436,10 @@ public function getCurrentIds() {
    * Returns -1 if the source is not countable.
    *
    * @param bool $refresh
-   *   (optional) Whether or not to refresh the count. Defaults to FALSE.
+   *   (optional) Whether or not to refresh the count. Defaults to FALSE. Not
+   *   all implementations support caching the counts. In such instance this
+   *   parameter is meaningless the result of calling the method will always be
+   *   up to date.
    *
    * @return int
    *   The count.
diff --git a/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
index 881e2fbcf6..35ab8abd85 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
@@ -365,7 +365,7 @@ protected function fetchNextBatch() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return $this->query()->countQuery()->execute()->fetchField();
   }
 
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/Variable.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/Variable.php
index 410acec229..e127dfbdc8 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/Variable.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/Variable.php
@@ -58,7 +58,7 @@ protected function values() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return intval($this->query()->countQuery()->execute()->fetchField() > 0);
   }
 
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/VariableTranslation.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/VariableTranslation.php
index 566a8402e0..f2ca8b73aa 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/VariableTranslation.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/VariableTranslation.php
@@ -68,7 +68,7 @@ protected function values() {
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return $this->initializeIterator()->count();
   }
 
diff --git a/core/modules/node/src/Plugin/migrate/source/d6/ViewModeBase.php b/core/modules/node/src/Plugin/migrate/source/d6/ViewModeBase.php
index 315f069a61..88d84d9524 100644
--- a/core/modules/node/src/Plugin/migrate/source/d6/ViewModeBase.php
+++ b/core/modules/node/src/Plugin/migrate/source/d6/ViewModeBase.php
@@ -12,7 +12,7 @@
   /**
    * {@inheritdoc}
    */
-  public function count() {
+  public function count($refresh = FALSE) {
     return count($this->initializeIterator());
   }