diff --git a/youtube_dl/extractor/vessel.py b/youtube_dl/extractor/vessel.py
index 2cd617b91c..5b7647f8a2 100644
--- a/youtube_dl/extractor/vessel.py
+++ b/youtube_dl/extractor/vessel.py
@@ -13,7 +13,7 @@ from ..utils import (
 
 
 class VesselIE(InfoExtractor):
-    _VALID_URL = r'https?://(?:www\.)?vessel\.com/(?:videos|embed)/(?P<id>[0-9a-zA-Z]+)'
+    _VALID_URL = r'https?://(?:www\.)?vessel\.com/(?:videos|embed)/(?P<id>[0-9a-zA-Z-_]+)'
     _API_URL_TEMPLATE = 'https://www.vessel.com/api/view/items/%s'
     _LOGIN_URL = 'https://www.vessel.com/api/account/login'
     _NETRC_MACHINE = 'vessel'
@@ -37,7 +37,7 @@ class VesselIE(InfoExtractor):
     @staticmethod
     def _extract_urls(webpage):
         return [url for _, url in re.findall(
-            r'<iframe[^>]+src=(["\'])((?:https?:)?//(?:www\.)?vessel\.com/embed/[0-9a-zA-Z]+.*?)\1',
+            r'<iframe[^>]+src=(["\'])((?:https?:)?//(?:www\.)?vessel\.com/embed/[0-9a-zA-Z-_]+.*?)\1',
             webpage)]
 
     @staticmethod