diff --git a/slackbuilder.cabal b/slackbuilder.cabal
index ca68bce..547fe90 100644
--- a/slackbuilder.cabal
+++ b/slackbuilder.cabal
@@ -29,6 +29,8 @@ common dependencies
     conduit ^>= 1.3.5,
     conduit-extra ^>= 1.3,
     http-client ^>= 0.7,
+    -- Workaround: 0.3.6.4 is broken, explicit dependency is otherwise not needed.
+    http-client-tls == 0.3.6.3,
     containers ^>= 0.6,
     cryptonite >= 0.30,
     directory ^>= 1.3.8,