diff --git a/theme/cornflower/docstyles.php b/theme/cornflower/docstyles.php
index 235aab2dcb5..5a4c4df2e56 100644
--- a/theme/cornflower/docstyles.php
+++ b/theme/cornflower/docstyles.php
@@ -1,13 +1,11 @@
 <?PHP /*  $Id$ */
 
 /// We use PHP so we can do value substitutions into the styles
-
-    if (!isset($themename)) {
-        $themename = NULL;
-    }
-
     $nomoodlecookie = true;
+
     require_once("../../config.php");
+    $themename = optional_param('themename', NULL, PARAM_SAFEDIR);
+
     $themeurl = style_sheet_setup(filemtime("styles.php"), 300, $themename);
 
 ///
diff --git a/theme/formal_white/docstyles.php b/theme/formal_white/docstyles.php
index a0fc8abeef1..296b28d3dff 100644
--- a/theme/formal_white/docstyles.php
+++ b/theme/formal_white/docstyles.php
@@ -1,13 +1,11 @@
 <?PHP /*  $Id$ */
 
 /// We use PHP so we can do value substitutions into the styles
-
-    if (!isset($themename)) {
-        $themename = NULL;
-    }
-
     $nomoodlecookie = true;
+
     require_once("../../config.php");
+    $themename = optional_param('themename', NULL, PARAM_SAFEDIR);
+
     $themeurl = style_sheet_setup(filemtime("styles.php"), 300, $themename);
 
 ///
diff --git a/theme/oceanblue/docstyles.php b/theme/oceanblue/docstyles.php
index 10db5de08ff..074d4554ea9 100644
--- a/theme/oceanblue/docstyles.php
+++ b/theme/oceanblue/docstyles.php
@@ -1,13 +1,11 @@
 <?PHP /*  $Id$ */
 
 /// We use PHP so we can do value substitutions into the styles
-
-    if (!isset($themename)) {
-        $themename = NULL;
-    }
-
     $nomoodlecookie = true;
+
     require_once("../../config.php");
+    $themename = optional_param('themename', NULL, PARAM_SAFEDIR);
+
     $themeurl = style_sheet_setup(filemtime("styles.php"), 300, $themename);
 
 ///
diff --git a/theme/orangewhite/docstyles.php b/theme/orangewhite/docstyles.php
index dd370bc9715..bb9976e44ec 100644
--- a/theme/orangewhite/docstyles.php
+++ b/theme/orangewhite/docstyles.php
@@ -1,13 +1,11 @@
 <?PHP /*  $Id$ */
 
 /// We use PHP so we can do value substitutions into the styles
-
-    if (!isset($themename)) {
-        $themename = NULL;
-    }
-
     $nomoodlecookie = true;
+
     require_once("../../config.php");
+    $themename = optional_param('themename', NULL, PARAM_SAFEDIR);
+
     $themeurl = style_sheet_setup(filemtime("styles.php"), 300, $themename);
 
 ///
diff --git a/theme/orangewhitepda/docstyles.php b/theme/orangewhitepda/docstyles.php
index dd370bc9715..bb9976e44ec 100644
--- a/theme/orangewhitepda/docstyles.php
+++ b/theme/orangewhitepda/docstyles.php
@@ -1,13 +1,11 @@
 <?PHP /*  $Id$ */
 
 /// We use PHP so we can do value substitutions into the styles
-
-    if (!isset($themename)) {
-        $themename = NULL;
-    }
-
     $nomoodlecookie = true;
+
     require_once("../../config.php");
+    $themename = optional_param('themename', NULL, PARAM_SAFEDIR);
+
     $themeurl = style_sheet_setup(filemtime("styles.php"), 300, $themename);
 
 ///
diff --git a/theme/standard/docstyles.php b/theme/standard/docstyles.php
index 235aab2dcb5..5a4c4df2e56 100644
--- a/theme/standard/docstyles.php
+++ b/theme/standard/docstyles.php
@@ -1,13 +1,11 @@
 <?PHP /*  $Id$ */
 
 /// We use PHP so we can do value substitutions into the styles
-
-    if (!isset($themename)) {
-        $themename = NULL;
-    }
-
     $nomoodlecookie = true;
+
     require_once("../../config.php");
+    $themename = optional_param('themename', NULL, PARAM_SAFEDIR);
+
     $themeurl = style_sheet_setup(filemtime("styles.php"), 300, $themename);
 
 ///