diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 0034ace70ca074c5484b1b624982fb2baad3a034..531357609c30ea0e88eaf05d559656364f4d6c4b 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -61,8 +61,6 @@ Drupal 7.50, xxxx-xx-xx (development version)
 - Made it possible to use any callable as an ajax form callback.
 - Made it possible to use any callable as menu access, menu theme, menu title
   and page delivery callback.
-- Made it possible to use any callable as a theme processor or theme function
-  callback.
 
 Drupal 7.44, 2016-06-15
 -----------------------
diff --git a/includes/theme.inc b/includes/theme.inc
index 991beea960fe8c181d0493fb2f6b17ecdc0e78f3..ff54d6e2c542fa9315bd1f7d4d897670b50e6e51 100644
--- a/includes/theme.inc
+++ b/includes/theme.inc
@@ -1119,7 +1119,7 @@ function theme($hook, $variables = array()) {
     foreach (array('preprocess functions', 'process functions') as $phase) {
       if (!empty($info[$phase])) {
         foreach ($info[$phase] as $processor_function) {
-          if (is_callable($processor_function)) {
+          if (function_exists($processor_function)) {
             // We don't want a poorly behaved process function changing $hook.
             $hook_clone = $hook;
             $processor_function($variables, $hook_clone);
@@ -1157,7 +1157,7 @@ function theme($hook, $variables = array()) {
   // Generate the output using either a function or a template.
   $output = '';
   if (isset($info['function'])) {
-    if (is_callable($info['function'])) {
+    if (function_exists($info['function'])) {
       $output = $info['function']($variables);
     }
   }