diff --git a/includes/file.inc b/includes/file.inc
index 7ec13f3..b7059b1 100644
--- a/includes/file.inc
+++ b/includes/file.inc
@@ -447,7 +447,7 @@ 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($directory);
   }
@@ -2112,6 +2112,25 @@ function file_get_mimetype($uri, $mapping = NULL) {
 }
 
 /**
+ * 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);
+}
+
+/**
  * Sets the permissions on a file or directory.
  *
  * This function will use the 'file_chmod_directory' and 'file_chmod_file'
@@ -2301,6 +2320,27 @@ function drupal_basename($uri, $suffix = NULL) {
 }
 
 /**
+ * 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));
+}
+
+/**
  * Creates a directory using Drupal's default mode.
  *
  * PHP's mkdir() does not respect Drupal's default permissions mode. If a mode
@@ -2438,7 +2478,7 @@ function file_directory_temp() {
     }
 
     foreach ($directories as $directory) {
-      if (is_dir($directory) && is_writable($directory)) {
+      if (is_dir($directory) && file_directory_is_writable($directory)) {
         $temporary_directory = $directory;
         break;
       }
diff --git a/includes/install.core.inc b/includes/install.core.inc
index ec3a853..4083f6b 100644
--- a/includes/install.core.inc
+++ b/includes/install.core.inc
@@ -1590,7 +1590,7 @@ function install_check_requirements($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/includes/install.inc b/includes/install.inc
index 6411f8f..afd22f7 100644
--- a/includes/install.inc
+++ b/includes/install.inc
@@ -852,7 +852,7 @@ 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)) {
               $return = FALSE;
             }
             break;
@@ -867,7 +867,7 @@ function drupal_verify_install_file($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)) {
               $return = FALSE;
             }
             break;
@@ -965,7 +965,7 @@ function drupal_install_fix_file($file, $mask, $message = TRUE) {
           }
           break;
         case FILE_EXECUTABLE:
-          if (!is_executable($file)) {
+          if (!drupal_is_executable($file)) {
             $mod |= 0111;
           }
           break;
@@ -980,7 +980,7 @@ function drupal_install_fix_file($file, $mask, $message = TRUE) {
           }
           break;
         case FILE_NOT_EXECUTABLE:
-          if (is_executable($file)) {
+          if (drupal_is_executable($file)) {
             $mod &= ~0111;
           }
           break;
diff --git a/includes/updater.inc b/includes/updater.inc
index d4f99e9..4b03a26 100644
--- a/includes/updater.inc
+++ b/includes/updater.inc
@@ -351,7 +351,7 @@ class Updater {
    *   If the chmod should be applied recursively.
    */
   public function makeWorldReadable(&$filetransfer, $path, $recursive = TRUE) {
-    if (!is_executable($path)) {
+    if (!drupal_is_executable($path)) {
       // Set it to read + execute.
       $new_perms = substr(sprintf('%o', fileperms($path)), -4, -1) . "5";
       $filetransfer->chmod($path, intval($new_perms, 8), $recursive);
diff --git a/modules/system/system.admin.inc b/modules/system/system.admin.inc
index fde0c28..b0b6351 100644
--- a/modules/system/system.admin.inc
+++ b/modules/system/system.admin.inc
@@ -1692,7 +1692,7 @@ function system_performance_settings() {
   );
 
   $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/modules/system/system.install b/modules/system/system.install
index 0b4e1fa..c655851 100644
--- a/modules/system/system.install
+++ b/modules/system/system.install
@@ -331,7 +331,7 @@ function system_requirements($phase) {
     if ($phase == 'install') {
       file_prepare_directory($directory, FILE_CREATE_DIRECTORY);
     }
-    $is_writable = is_writable($directory);
+    $is_writable = file_directory_is_writable($directory);
     $is_directory = is_dir($directory);
     if (!$is_writable || !$is_directory) {
       $description = '';
diff --git a/modules/system/system.module b/modules/system/system.module
index 072850e..d36393f 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -2163,7 +2163,7 @@ function system_check_directory($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);
diff --git a/modules/user/user.test b/modules/user/user.test
index b5b64d6..7664d3b 100644
--- a/modules/user/user.test
+++ b/modules/user/user.test
@@ -877,7 +877,7 @@ class UserPictureTestCase extends DrupalWebTestCase {
     $picture_path = $file_dir . $picture_dir;
 
     $pic_check = file_prepare_directory($picture_path, FILE_CREATE_DIRECTORY);
-    $this->_directory_test = is_writable($picture_path);
+    $this->_directory_test = file_directory_is_writable($picture_path);
     $this->assertTrue($this->_directory_test, "The directory $picture_path doesn't exist or is not writable. Further tests won't be made.");
   }