diff --git a/kallithea/lib/pygmentsutils.py b/kallithea/lib/pygmentsutils.py
--- a/kallithea/lib/pygmentsutils.py
+++ b/kallithea/lib/pygmentsutils.py
@@ -78,3 +78,15 @@ def get_index_filenames():
             filenames.append(f)
 
     return filenames
+
+
+def get_custom_lexer(extension):
+    """
+    returns a custom lexer if it's defined in rcextensions module, or None
+    if there's no custom lexer defined
+    """
+    import kallithea
+    #check if we didn't define this extension as other lexer
+    if kallithea.EXTENSIONS and extension in kallithea.EXTENSIONS.EXTRA_LEXERS:
+        _lexer_name = kallithea.EXTENSIONS.EXTRA_LEXERS[extension]
+        return lexers.get_lexer_by_name(_lexer_name)