diff --git a/dev/install/install.php5 b/dev/install/install.php5
index d0d75003a..1d567df1c 100644
--- a/dev/install/install.php5
+++ b/dev/install/install.php5
@@ -476,6 +476,7 @@ class InstallRequirements {
 		// special case for display_errors, check the original value before
 		// it was changed at the start of this script.
 		if($settingName = 'display_errors') {
+			global $originalDisplayErrorsValue;
 			$val = $originalDisplayErrorsValue;
 		} else {
 			$val = ini_get($settingName);