diff --git a/files/classes/converter.php b/files/classes/converter.php
index 32793d3485e..da8c5ba0cbd 100644
--- a/files/classes/converter.php
+++ b/files/classes/converter.php
@@ -127,7 +127,7 @@ class converter {
         if ($status === conversion::STATUS_PENDING || $status === conversion::STATUS_FAILED) {
             // The current status is either pending or failed.
             // Attempt to pick up a new converter and convert the document.
-            $from = \core_filetypes::get_file_extension($file->get_mimetype());
+            $from = pathinfo($file->get_filename(), PATHINFO_EXTENSION);
             $converters = $this->get_document_converter_classes($from, $format);
             $currentconverter = $this->get_next_converter($converters, $conversion->get('converter'));
 
@@ -225,9 +225,9 @@ class converter {
             return false;
         }
 
-        $from = \core_filetypes::get_file_extension($file->get_mimetype());
+        $from = pathinfo($file->get_filename(), PATHINFO_EXTENSION);
         if (!$from) {
-            // No mime type could be found. Unable to determine converter.
+            // No file extension could be found. Unable to determine converter.
             return false;
         }
 
diff --git a/files/tests/converter_test.php b/files/tests/converter_test.php
index 950d5932df0..e345c1e40d9 100644
--- a/files/tests/converter_test.php
+++ b/files/tests/converter_test.php
@@ -341,7 +341,7 @@ class core_files_converter_testcase extends advanced_testcase {
     }
 
     /**
-     * Test the can_convert_storedfile_to function with a file with indistinguished mimetype.
+     * Test the can_convert_storedfile_to function with a file with a known mimetype and extension.
      */
     public function test_can_convert_storedfile_to_docx() {
         $returnvalue = (object) [];
@@ -352,8 +352,7 @@ class core_files_converter_testcase extends advanced_testcase {
 
         $types = \core_filetypes::get_types();
 
-        // A file with filename '.' is a directory.
-        $file = $this->get_stored_file('example content', 'example', [
+        $file = $this->get_stored_file('example content', 'example.docx', [
                 'mimetype' => $types['docx']['type'],
             ]);