diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 697647be..b2330298 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -7,7 +7,9 @@ jobs:
       fail-fast: false
       matrix:
         os:
-        - ubuntu-latest
+        # Until https://github.com/ocaml/setup-ocaml/issues/872.
+        # When fixing, search for other instances of this string in this file.
+        - ubuntu-22.04
         ocaml:
         - 5.2.x
         - 4.14.x
@@ -68,7 +70,7 @@ jobs:
       fail-fast: false
       matrix:
         os:
-        - ubuntu-latest
+        - ubuntu-22.04
         ocaml:
         - 5.2.x
         - 4.14.x
@@ -100,7 +102,7 @@ jobs:
 
   mirage:
     if: false
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v4
       with: