diff --git a/tests/pathogen-embed-umap-with-distances.t b/tests/pathogen-embed-umap-with-distances.t
index b10e1ec..f19f67f 100644
--- a/tests/pathogen-embed-umap-with-distances.t
+++ b/tests/pathogen-embed-umap-with-distances.t
@@ -1,3 +1,7 @@
+Always use the simplest Numba threading layer, to avoid lower-level OMP warnings.
+
+  $ export NUMBA_THREADING_LAYER=workqueue
+
 Get a distance matrix from a H3N2 HA alignment.
 
   $ pathogen-distance \
diff --git a/tests/pathogen-embed-umap.t b/tests/pathogen-embed-umap.t
index 4d75c0d..41b66b7 100644
--- a/tests/pathogen-embed-umap.t
+++ b/tests/pathogen-embed-umap.t
@@ -1,3 +1,7 @@
+Always use the simplest Numba threading layer, to avoid lower-level OMP warnings.
+
+  $ export NUMBA_THREADING_LAYER=workqueue
+
 Run pathogen-embed with UMAP on a H3N2 HA alignment.
 
   $ pathogen-embed \