diff --git a/modules/image/image.test b/modules/image/image.test
index 3591979..fa7b013 100644
--- a/modules/image/image.test
+++ b/modules/image/image.test
@@ -184,6 +184,29 @@ class ImageStylesPathAndUrlTestCase extends DrupalWebTestCase {
   }
 
   /**
+   * Test that we do not pass an array to drupal_add_http_header.
+   */
+  function testImageContentTypeHeaders() {
+    $files = $this->drupalGetTestFiles('image');
+    $file = array_shift($files);
+    // Copy the test file to private folder.
+    $private_file = file_copy($file, 'private://', FILE_EXISTS_RENAME);
+    // Tell image_module_test module to return the headers we want to test.
+    variable_set('image_module_test_invalid_headers', $private_file->uri);
+    // Invoke image_style_deliver so it will try to set headers.
+    $generated_url = image_style_url($this->style_name, $private_file->uri);
+    $this->drupalGet($generated_url);
+    // Check that we did not get a notice in watchdog.
+    $last_message = db_select('watchdog', 'w')
+      ->fields('w', array('variables'))
+      ->orderBy('wid', 'DESC')
+      ->execute()
+      ->fetchAssoc();
+    $this->assertFalse(strpos($last_message['variables'], 'Array to string conversion') > 0);
+    variable_del('image_module_test_invalid_headers');
+  }
+
+  /**
    * Test image_style_url().
    */
   function _testImageStyleUrlAndPath($scheme, $clean_url = TRUE, $extra_slash = FALSE) {
diff --git a/modules/image/tests/image_module_test.module b/modules/image/tests/image_module_test.module
index 8a322fb..cf49618 100644
--- a/modules/image/tests/image_module_test.module
+++ b/modules/image/tests/image_module_test.module
@@ -9,6 +9,9 @@ function image_module_test_file_download($uri) {
   if (variable_get('image_module_test_file_download', FALSE) == $uri) {
     return array('X-Image-Owned-By' => 'image_module_test');
   }
+  if (variable_get('image_module_test_invalid_headers', FALSE) == $uri) {
+    return array('Content-Type' => 'image/jpg');
+  }
 }
 
 /**