diff --git a/core/lib/Drupal/Core/Image/Image.php b/core/lib/Drupal/Core/Image/Image.php
index 3d99b21..3c4553f 100644
--- a/core/lib/Drupal/Core/Image/Image.php
+++ b/core/lib/Drupal/Core/Image/Image.php
@@ -104,9 +104,11 @@ public function getExtension() {
 
     // Extension may still be empty after calling processInfo(). This happens if
     // the image doesn't exists yet on disk, but only in memory as image
-    // resource. Try to extact the extension from the image source path.
-    if (empty($this->extension)) {
-      $this->extension = pathinfo($this->getSource(), PATHINFO_EXTENSION);
+    // resource. Try to extract the extension from the image source path.
+    if (empty($this->extension) && ($extension = pathinfo($this->getSource(), PATHINFO_EXTENSION))) {
+      if (in_array($extension, array('gif', 'jpg', 'png'))) {
+        $this->extension = $extension;
+      }
     }
 
     return $this->extension;