diff --git a/filter/algebra/algebradebug.php b/filter/algebra/algebradebug.php
index 6ae4967107b..c1b04acc824 100644
--- a/filter/algebra/algebradebug.php
+++ b/filter/algebra/algebradebug.php
@@ -7,6 +7,14 @@
 
     require_once("../../config.php");
 
+    if (empty($CFG->textfilters)) {
+        error ('Filter not enabled!');
+    } else {
+        $filters = explode(',', $CFG->textfilters);
+        if (array_search('filter/algebra', $filters) === FALSE) {
+            error ('Filter not enabled!');
+        }
+    }
 
     $CFG->texfilterdir = "filter/tex";
     $CFG->algebrafilterdir = "filter/algebra";
diff --git a/filter/algebra/pix.php b/filter/algebra/pix.php
index d0218474d86..8fd51bff894 100644
--- a/filter/algebra/pix.php
+++ b/filter/algebra/pix.php
@@ -6,6 +6,16 @@
     $nomoodlecookie = true;     // Because it interferes with caching
 
     require_once('../../config.php');
+
+    if (empty($CFG->textfilters)) {
+        error ('Filter not enabled!');
+    } else {
+        $filters = explode(',', $CFG->textfilters);
+        if (array_search('filter/algebra', $filters) === FALSE) {
+            error ('Filter not enabled!');
+        }
+    }
+
     require_once($CFG->libdir.'/filelib.php');
 
     $CFG->texfilterdir     = 'filter/tex';
diff --git a/filter/tex/pix.php b/filter/tex/pix.php
index 0b79fba73f8..1977c8eb887 100644
--- a/filter/tex/pix.php
+++ b/filter/tex/pix.php
@@ -6,6 +6,16 @@
     $nomoodlecookie = true;     // Because it interferes with caching
 
     require_once('../../config.php');
+
+    if (empty($CFG->textfilters)) {
+        error ('Filter not enabled!');
+    } else {
+        $filters = explode(',', $CFG->textfilters);
+        if (array_search('filter/tex', $filters) === FALSE) {
+            error ('Filter not enabled!');
+        }
+    }
+
     require_once($CFG->libdir.'/filelib.php');
     require_once('defaultsettings.php' );
     require_once('latex.php');
diff --git a/filter/tex/texdebug.php b/filter/tex/texdebug.php
index d6e41ae49f2..2db14a7c732 100644
--- a/filter/tex/texdebug.php
+++ b/filter/tex/texdebug.php
@@ -7,6 +7,15 @@
 
     require_once("../../config.php");
 
+    if (empty($CFG->textfilters)) {
+        error ('Filter not enabled!');
+    } else {
+        $filters = explode(',', $CFG->textfilters);
+        if (array_search('filter/tex', $filters) === FALSE) {
+            error ('Filter not enabled!');
+        }
+    }
+
     $CFG->texfilterdir = "filter/tex";
     $CFG->teximagedir = "filter/tex";
 
diff --git a/filter/tex/texed.php b/filter/tex/texed.php
index 5d61b119354..c0069428f46 100644
--- a/filter/tex/texed.php
+++ b/filter/tex/texed.php
@@ -7,6 +7,15 @@
 
     require_once("../../config.php");
 
+    if (empty($CFG->textfilters)) {
+        error ('Filter not enabled!');
+    } else {
+        $filters = explode(',', $CFG->textfilters);
+        if (array_search('filter/tex', $filters) === FALSE) {
+            error ('Filter not enabled!');
+        }
+    }
+
     $CFG->texfilterdir = "filter/tex";
     $CFG->teximagedir = "filter/tex";