diff --git a/assets/checksums.txt b/assets/checksums.txt
index 8b2341c01..27cd783dc 100644
--- a/assets/checksums.txt
+++ b/assets/checksums.txt
@@ -1,7 +1,7 @@
 363904dff57e330919eada2e0e793a79 assets/ublock/unbreak.txt
 c91286a3e6dc3136bc6e078d5c0db4d0 assets/ublock/redirect-resources.txt
 6c077d6d5b39e8a5a407966ad62c9c32 assets/ublock/privacy.txt
-b0a57e326035b44bfceb2b038030e391 assets/ublock/filters.txt
+c5657db2c775d8f7540909b4f712548e assets/ublock/filters.txt
 146704ad1c0393e342afdb416762c183 assets/ublock/badware.txt
 4b95ee2fe4c3f1c5258cc1afd9cbf677 assets/ublock/redirect.txt
 e1a6bb625a9ee59cc57f6b77c76108ff assets/ublock/filter-lists.json
diff --git a/assets/ublock/filters.txt b/assets/ublock/filters.txt
index 03a2e602f..e99ae10a2 100644
--- a/assets/ublock/filters.txt
+++ b/assets/ublock/filters.txt
@@ -195,3 +195,9 @@ segmentnext.com###content > div > div[class] > div[class] > div[class]
 
 # http://forum.palemoon.org/viewtopic.php?f=46&t=10271#p71697
 ||cdn.windows7themes.net/wp-content/advert.js$script,first-party
+
+# https://github.com/gorhill/uBlock/issues/991
+# New `popunder` filter option to explicitly block popunders.
+# Older version of uBO will discard this unknown filter option -- so it's safe
+# to add it here now.
+|http://$popunder,third-party,domain=xhamster.com