diff --git a/core/includes/file.inc b/core/includes/file.inc
index 534d211..f362961 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -507,7 +507,7 @@ function file_prepare_directory(&$directory, $options = FILE_MODIFY_PERMISSIONS)
     return FALSE;
   }
   // The directory exists, so check to see if it is writable.
-  $writable = is_writable($directory);
+  $writable = file_directory_is_writable($directory);
   if (!$writable && ($options & FILE_MODIFY_PERMISSIONS)) {
     return drupal_chmod($directory);
   }
@@ -1919,7 +1919,7 @@ function file_directory_os_temp() {
   $directories[] = sys_get_temp_dir();
 
   foreach ($directories as $directory) {
-    if (is_dir($directory) && is_writable($directory)) {
+    if (is_dir($directory) && file_directory_is_writable($directory)) {
       return $directory;
     }
   }
@@ -1927,5 +1927,45 @@ function file_directory_os_temp() {
 }
 
 /**
+ * Determines if a directory is writable by the web server.
+ *
+ * In order to be able to write files within the directory, the directory
+ * itself must be writable, and it must also have the executable bit set. This
+ * helper function checks both at the same time.
+ *
+ * @param $uri
+ *   A URI or pathname pointing to the directory that will be checked.
+ *
+ * @return
+ *   TRUE if the directory is writable and executable; FALSE otherwise.
+ */
+function file_directory_is_writable($uri) {
+  // By converting the URI to a normal path using drupal_realpath(), we can
+  // correctly handle both stream wrappers and normal paths.
+  return is_writable(drupal_realpath($uri)) && drupal_is_executable($uri);
+}
+
+/**
+ * Determines if a file or directory is executable.
+ *
+ * PHP's is_executable() does not fully support stream wrappers, so this
+ * function fills that gap.
+ *
+ * @param $uri
+ *   A URI or pathname pointing to the file or directory that will be checked.
+ *
+ * @return
+ *   TRUE if the file or directory is executable; FALSE otherwise.
+ *
+ * @see is_executable()
+ * @ingroup php_wrappers
+ */
+function drupal_is_executable($uri) {
+  // By converting the URI to a normal path using drupal_realpath(), we can
+  // correctly handle both stream wrappers and normal paths.
+  return is_executable(drupal_realpath($uri));
+}
+
+/**
  * @} End of "defgroup file".
  */
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index c4de9ee..f609ce5 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1910,7 +1910,7 @@ function install_check_translations($install_state) {
   // Get values so the requirements errors can be specific.
   if (drupal_verify_install_file($translations_directory, FILE_EXIST|FILE_WRITABLE, 'dir')) {
     $readable = is_readable($translations_directory);
-    $writable = is_writable($translations_directory);
+    $writable = file_directory_is_writable($translations_directory);
     $translations_directory_exists = TRUE;
   }
 
@@ -2074,7 +2074,7 @@ function install_check_requirements($install_state) {
     // Otherwise, if settings.php does not exist yet, we can try to copy
     // default.settings.php to create it.
     elseif (!$exists) {
-      $copied = drupal_verify_install_file($conf_path, FILE_EXIST|FILE_WRITABLE, 'dir') && @copy($default_settings_file, $settings_file);
+      $copied = drupal_verify_install_file($conf_path, FILE_EXIST|FILE_WRITABLE|FILE_EXECUTABLE, 'dir') && @copy($default_settings_file, $settings_file);
       if ($copied) {
         // If the new settings file has the same owner as default.settings.php,
         // this means default.settings.php is owned by the webserver user.
diff --git a/core/includes/install.inc b/core/includes/install.inc
index d33bb0a..c74e99f 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -316,7 +316,7 @@ function install_verify_config_directory($type) {
   // prepared settings.php that defines $config_directories already.
   try {
     $config_directory = config_get_config_directory($type);
-    if (is_dir($config_directory) && is_writable($config_directory)) {
+    if (is_dir($config_directory) && file_directory_is_writable($config_directory)) {
       return TRUE;
     }
   }
@@ -493,7 +493,7 @@ function drupal_verify_install_file($file, $mask = NULL, $type = 'file') {
             }
             break;
           case FILE_EXECUTABLE:
-            if (!is_executable($file) && !drupal_install_fix_file($file, $mask)) {
+            if (!drupal_is_executable($file) && !drupal_install_fix_file($file, $mask)) {
               $return = FALSE;
             }
             break;
@@ -508,7 +508,7 @@ function drupal_verify_install_file($file, $mask = NULL, $type = 'file') {
             }
             break;
           case FILE_NOT_EXECUTABLE:
-            if (is_executable($file) && !drupal_install_fix_file($file, $mask)) {
+            if (drupal_is_executable($file) && !drupal_install_fix_file($file, $mask)) {
               $return = FALSE;
             }
             break;
@@ -608,7 +608,7 @@ function drupal_install_fix_file($file, $mask, $message = TRUE) {
           }
           break;
         case FILE_EXECUTABLE:
-          if (!is_executable($file)) {
+          if (!drupal_is_executable($file)) {
             $mod |= 0111;
           }
           break;
@@ -623,7 +623,7 @@ function drupal_install_fix_file($file, $mask, $message = TRUE) {
           }
           break;
         case FILE_NOT_EXECUTABLE:
-          if (is_executable($file)) {
+          if (drupal_is_executable($file)) {
             $mod &= ~0111;
           }
           break;
diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index b483e7e..d984701 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -1662,7 +1662,7 @@ function system_performance_settings($form, &$form_state) {
   );
 
   $directory = 'public://';
-  $is_writable = is_dir($directory) && is_writable($directory);
+  $is_writable = is_dir($directory) && file_directory_is_writable($directory);
   $disabled = !$is_writable;
   $disabled_message = '';
   if (!$is_writable) {
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 7f621d4..be81f1c 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -370,7 +370,7 @@ function system_requirements($phase) {
     if ($phase == 'install') {
       file_prepare_directory($directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
     }
-    $is_writable = is_writable($directory);
+    $is_writable = file_directory_is_writable($directory);
     $is_directory = is_dir($directory);
     if (!$is_writable || !$is_directory) {
       $description = '';
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 1a659c5..8229366 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2726,7 +2726,7 @@ function system_check_directory($form_element) {
     watchdog('file system', 'The directory %directory does not exist and could not be created.', array('%directory' => $directory), WATCHDOG_ERROR);
   }
 
-  if (is_dir($directory) && !is_writable($directory) && !drupal_chmod($directory)) {
+  if (is_dir($directory) && !file_directory_is_writable($directory) && !drupal_chmod($directory)) {
     // If the directory is not writable and cannot be made so.
     form_set_error($form_element['#parents'][0], t('The directory %directory exists but is not writable and could not be made writable.', array('%directory' => $directory)));
     watchdog('file system', 'The directory %directory exists but is not writable and could not be made writable.', array('%directory' => $directory), WATCHDOG_ERROR);