diff --git a/webvtt/parsers.py b/webvtt/parsers.py
index 3a978ca..2676c3a 100644
--- a/webvtt/parsers.py
+++ b/webvtt/parsers.py
@@ -155,7 +155,10 @@ class WebVTTParser(TextBasedParser):
     WebVTT parser.
     """
 
-    TIMEFRAME_LINE_PATTERN = re.compile(r'\s*((?:\d+:)?\d{2}:\d{2}.\d{3})\s*-->\s*((?:\d+:)?\d{2}:\d{2}.\d{3})')
+    TIMEFRAME_LINE_PATTERN = re.compile(
+        # matches timestamp format: 0:0:13.540 --> 0:0:17.850
+        r'\s*((?:\d+:)?\d{1,2}:\d{1,2}.\d{3})\s*-->\s*((?:\d+:)?\d{1,2}:\d{1,2}.\d{3})'
+    )
     COMMENT_PATTERN = re.compile(r'NOTE(?:\s.+|$)')
     STYLE_PATTERN = re.compile(r'STYLE[ \t]*$')