diff --git a/.htaccess b/.htaccess
index fd7bd29..cc2d338 100644
--- a/.htaccess
+++ b/.htaccess
@@ -35,10 +35,13 @@ AddEncoding gzip svgz
 
 # PHP 5, Apache 1 and 2.
 <IfModule mod_php5.c>
-  php_flag session.auto_start               off
-  php_value mbstring.http_input             pass
-  php_value mbstring.http_output            pass
-  php_flag mbstring.encoding_translation    off
+  php_flag session.auto_start off
+  php_value mbstring.http_input pass
+  php_value mbstring.http_output pass
+  php_flag mbstring.encoding_translation off
+  # PHP 5.6 has deprecated $HTTP_RAW_POST_DATA and produces warnings if this is
+  # not set.
+  php_value always_populate_raw_post_data -1
 </IfModule>
 
 # Requires mod_expires to be enabled.
diff --git a/core/modules/rest/src/Tests/CreateTest.php b/core/modules/rest/src/Tests/CreateTest.php
index d125f1b..eac6ad4 100644
--- a/core/modules/rest/src/Tests/CreateTest.php
+++ b/core/modules/rest/src/Tests/CreateTest.php
@@ -302,6 +302,8 @@ public function createAccountPerEntity($entity_type) {
    *   The body for the POST request.
    */
   public function assertCreateEntityOverRestApi($entity_type, $serialized = NULL) {
+    // Note: this will fail if using PHP 5.6 and 'always_populate_raw_post_data'
+    // set to something other than '-1'. See https://www.drupal.org/node/2456025.
     $this->httpRequest('entity/' . $entity_type, 'POST', $serialized, $this->defaultMimeType);
     $this->assertResponse(201);
   }
diff --git a/core/modules/rest/src/Tests/CsrfTest.php b/core/modules/rest/src/Tests/CsrfTest.php
index a686f448..14e1a80 100644
--- a/core/modules/rest/src/Tests/CsrfTest.php
+++ b/core/modules/rest/src/Tests/CsrfTest.php
@@ -80,6 +80,8 @@ public function testCookieAuth() {
     $curl_options = $this->getCurlOptions();
 
     // Try to create an entity without the CSRF token.
+    // Note: this will fail if using PHP 5.6 and 'always_populate_raw_post_data'
+    // set to something other than '-1'. See https://www.drupal.org/node/2456025.
     $this->curlExec($curl_options);
     $this->assertResponse(403);
     // Ensure that the entity was not created.