diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index fba8bcc033..1fa645896f 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -1326,9 +1326,8 @@ function media_upload_form( $errors = null ) {
 
 ?></div>
 <?php
-// Check quota for this blog if multisite
 if ( is_multisite() && !is_upload_space_available() ) {
-	echo '<p>' . sprintf( __( 'Sorry, you have filled your storage quota (%s MB).' ), get_space_allowed() ) . '</p>';
+	do_action( 'upload_ui_over_quota' );
 	return;
 }
 
@@ -2065,6 +2064,10 @@ function media_upload_flash_bypass() {
 }
 add_action('post-plupload-upload-ui', 'media_upload_flash_bypass');
 
+function multisite_over_quota_message() {
+	echo '<p>' . sprintf( __( 'Sorry, you have used all of your storage quota of %s MB.' ), get_space_allowed() ) . '</p>';
+}
+
 /**
  * {@internal Missing Short Description}}
  *
diff --git a/wp-includes/ms-default-filters.php b/wp-includes/ms-default-filters.php
index 44d8294ac5..45410143d6 100644
--- a/wp-includes/ms-default-filters.php
+++ b/wp-includes/ms-default-filters.php
@@ -45,6 +45,7 @@ add_filter( 'wp_upload_bits', 'upload_is_file_too_big' );
 add_filter( 'import_upload_size_limit', 'fix_import_form_size' );
 add_filter( 'upload_mimes', 'check_upload_mimes' );
 add_filter( 'upload_size_limit', 'upload_size_limit_filter' );
+add_action( 'upload_ui_over_quota', 'multisite_over_quota_message' );
 
 // Mail
 add_action( 'phpmailer_init', 'fix_phpmailer_messageid' );