diff --git a/core/lib/Drupal/Core/StreamWrapper/LocalReadOnlyStream.php b/core/lib/Drupal/Core/StreamWrapper/LocalReadOnlyStream.php
index 49a6596..1b14280 100644
--- a/core/lib/Drupal/Core/StreamWrapper/LocalReadOnlyStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/LocalReadOnlyStream.php
@@ -12,8 +12,8 @@
  *
  * This class extends the complete stream wrapper implementation in LocalStream.
  * URIs such as "public://example.txt" are expanded to a normal filesystem path
- * such as "sites/default/files/example.txt" and then PHP filesystem functions are
- * invoked.
+ * such as "sites/default/files/example.txt" and then PHP filesystem functions
+ * are invoked.
  *
  * Drupal\Core\StreamWrapper\LocalReadOnlyStream implementations need to
  * implement at least the getDirectoryPath() and getExternalUrl() methods.
@@ -41,9 +41,7 @@
    */
   public function stream_open($uri, $mode, $options, &$opened_path) {
     if ($mode != "r") {
-      debug("Write mode detected.");
       if ($options & STREAM_REPORT_ERRORS) {
-        debug("Report errors detected.");
         trigger_error('stream_open() write modes not supported for read-only stream wrappers', E_USER_WARNING);
       }
       return FALSE;
@@ -52,7 +50,7 @@ public function stream_open($uri, $mode, $options, &$opened_path) {
     $this->uri = $uri;
     $path = $this->getLocalPath();
     $this->handle = ($options & STREAM_REPORT_ERRORS) ? fopen($path, $mode) : @fopen($path, $mode);
-    if ((bool) $this->handle && $options & STREAM_USE_PATH) {
+    if ($this->handle !== FALSE && ($options & STREAM_USE_PATH)) {
       $opened_path = $path;
     }
 
@@ -70,21 +68,23 @@ public function stream_open($uri, $mode, $options, &$opened_path) {
    *   - LOCK_SH to acquire a shared lock (reader).
    *   - LOCK_EX to acquire an exclusive lock (writer).
    *   - LOCK_UN to release a lock (shared or exclusive).
-   *   - LOCK_NB if you don't want flock() to block while locking (not
-   *     supported on Windows).
+   *   - LOCK_NB added as a bitmask if you don't want flock() to block while
+   *     locking (not supported on Windows).
    *
    * @return bool
    *   Return FALSE for an exclusive lock (writer), as this is a read-only
-   *   stream wrapper.  Return TRUE for all other valid $operations.
+   *   stream wrapper.  Return the result of flock() for other valid operations.
+   *   Defaults to TRUE if an invalid operation is passed.
    *
    * @see http://php.net/manual/streamwrapper.stream-lock.php
    */
   public function stream_lock($operation) {
-    if (in_array($operation, array(LOCK_EX, LOCK_EX | LOCK_NB))) {
+    // Disallow exclusive lock or non-blocking lock requests
+    if (in_array($operation, array(LOCK_EX, LOCK_EX|LOCK_NB))) {
       trigger_error('stream_lock() exclusive lock operations not supported for read-only stream wrappers', E_USER_WARNING);
       return FALSE;
     }
-    if (in_array($operation, array(LOCK_SH, LOCK_UN, LOCK_NB))) {
+    if (in_array($operation, array(LOCK_SH, LOCK_UN, LOCK_SH|LOCK_NB))) {
       return flock($this->handle, $operation);
     }
 
@@ -208,9 +208,15 @@ public function rmdir($uri, $options) {
   }
 
   /**
-   * Implements Drupal\Core\StreamWrapper\StreamWrapperInterface::chmod().
+   * Support for chmod().
    *
    * Does not change file permissions as this is a read-only stream wrapper.
+   *
+   * @param int $mode
+   *   Permission flags - see chmod().
+   *
+   * @return bool
+   *   FALSE as the permission change will never be allowed.
    */
   public function chmod($mode) {
     trigger_error('chmod() not supported for read-only stream wrappers', E_USER_WARNING);
diff --git a/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php b/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php
index 950ba34..2ebcc06 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ReadOnlyStream.php
@@ -86,7 +86,7 @@ public function stream_open($uri, $mode, $options, &$opened_path) {
     $path = $this->getLocalPath();
     $this->handle = ($options & STREAM_REPORT_ERRORS) ? fopen($path, $mode) : @fopen($path, $mode);
 
-    if ((bool) $this->handle && $options & STREAM_USE_PATH) {
+    if ($this->handle !== FALSE && ($options & STREAM_USE_PATH)) {
       $opened_path = $path;
     }
 
@@ -109,16 +109,17 @@ public function stream_open($uri, $mode, $options, &$opened_path) {
    *
    * @return bool
    *   Return FALSE for an exclusive lock (writer), as this is a read-only
-   *   stream wrapper.  Return TRUE for all other valid $operations.
+   *   stream wrapper.  Return the result of flock() for other valid operations.
+   *   Defaults to TRUE if an invalid operation is passed.
    *
    * @see http://php.net/manual/streamwrapper.stream-lock.php
    */
   public function stream_lock($operation) {
-    if (in_array($operation, array(LOCK_EX, LOCK_EX | LOCK_NB))) {
+    if (in_array($operation, array(LOCK_EX, LOCK_EX|LOCK_NB))) {
       trigger_error('stream_lock() exclusive lock operations not supported for read-only stream wrappers', E_USER_WARNING);
       return FALSE;
     }
-    if (in_array($operation, array(LOCK_SH, LOCK_UN, LOCK_NB))) {
+    if (in_array($operation, array(LOCK_SH, LOCK_UN, LOCK_SH|LOCK_NB))) {
       return flock($this->handle, $operation);
     }
 
@@ -241,9 +242,15 @@ public function rmdir($uri, $options) {
   }
 
   /**
-   * Implements Drupal\Core\StreamWrapper\StreamWrapperInterface::chmod().
+   * Support for chmod().
    *
    * Does not change file permissions as this is a read-only stream wrapper.
+   *
+   * @param int $mode
+   *   Permission flags - see chmod().
+   *
+   * @return bool
+   *   FALSE as the permission change will never be allowed.
    */
   public function chmod($mode) {
     trigger_error('chmod() not supported for read-only stream wrappers', E_USER_WARNING);