diff --git a/pkgs/applications/version-management/mercurial/default.nix b/pkgs/applications/version-management/mercurial/default.nix
index b0d7c26abdd6..8320491758ea 100644
--- a/pkgs/applications/version-management/mercurial/default.nix
+++ b/pkgs/applications/version-management/mercurial/default.nix
@@ -77,7 +77,8 @@ let
       test-check-shbang.t
       EOF
 
-      export HGTESTFLAGS="--blacklist blacklists/nix"
+      # extended timeout necessary for tests to pass on the busy CI workers
+      export HGTESTFLAGS="--blacklist blacklists/nix --timeout 600"
       make check
     '';