diff --git a/theme/image.php b/theme/image.php
index e00f5592f7f..a1a2e66b360 100644
--- a/theme/image.php
+++ b/theme/image.php
@@ -24,6 +24,10 @@
  */
 
 
+// disable moodle specific debug messages and any errors in output,
+// comment out when debugging or better look into error log!
+define('NO_DEBUG_DISPLAY', true);
+
 // we need just the values from config.php and minlib.php
 define('ABORT_AFTER_CONFIG', true);
 require('../config.php'); // this stops immediately at the beginning of lib/setup.php
diff --git a/theme/javascript.php b/theme/javascript.php
index 6e8a79d785b..afe5d013124 100644
--- a/theme/javascript.php
+++ b/theme/javascript.php
@@ -24,6 +24,10 @@
  */
 
 
+// disable moodle specific debug messages and any errors in output,
+// comment out when debugging or better look into error log!
+define('NO_DEBUG_DISPLAY', true);
+
 // we need just the values from config.php and minlib.php
 define('ABORT_AFTER_CONFIG', true);
 require('../config.php'); // this stops immediately at the beginning of lib/setup.php
diff --git a/theme/styles.php b/theme/styles.php
index 6fcde59e1b6..909bfb5468c 100644
--- a/theme/styles.php
+++ b/theme/styles.php
@@ -24,6 +24,10 @@
  */
 
 
+// disable moodle specific debug messages and any errors in output,
+// comment out when debugging or better look into error log!
+define('NO_DEBUG_DISPLAY', true);
+
 // we need just the values from config.php and minlib.php
 define('ABORT_AFTER_CONFIG', true);
 require('../config.php'); // this stops immediately at the beginning of lib/setup.php