diff --git a/.gitlab/ci/thallium.sh b/.gitlab/ci/thallium.sh
index 8c389661f87b24d3b3c8b0f1a0626a2befcbf980..9ee9a45073b26a079c77061c3922fb0a910e4939 100755
--- a/.gitlab/ci/thallium.sh
+++ b/.gitlab/ci/thallium.sh
@@ -76,7 +76,7 @@ packages:
       prefix: /usr
 EOF
 
-readonly spec="mochi-thallium@0.10.1 ^libfabric fabrics=tcp,rxm,sockets ^mochi-margo@0.9.10 ^mercury@2.2.0"
+readonly spec="mochi-thallium@0.10.1 ^libfabric fabrics=tcp,rxm,sockets ^mochi-margo@0.9.10 ^mercury@2.2.0 ^argobots@dce6e727ffc4ca5b3ffc04cb9517c6689be51ec5=main"
 # inspect spec
 spack -C "$spackroot/config" spec $spec