diff --git a/pygrok/pygrok.py b/pygrok/pygrok.py
index 26a51c9..2006610 100644
--- a/pygrok/pygrok.py
+++ b/pygrok/pygrok.py
@@ -51,7 +51,7 @@ def grok_match(text, pattern, custom_patterns = {}, custom_patterns_dir = None):
         py_regex_pattern = re.sub(r'%{(\w+)}',
             lambda m: "(" + all_patterns[m.group(1)].regex_str + ")", py_regex_pattern)
 
-        if re.search('%{\w+}', py_regex_pattern) is None:
+        if re.search('%{\w+(:\w+)?}', py_regex_pattern) is None:
             break
 
     match_obj = re.search(py_regex_pattern, text)