diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 425568f..3a536d8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,7 +29,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest]
+        # ruby/setup-ruby has no Ruby 3.1 build for ubuntu-26.04, which ubuntu-latest now is
+        os: [ubuntu-24.04]
         ruby: ["3.1", "3.2", "3.3", "3.4", "4.0"]
         include:
           - os: macos-latest
@@ -51,7 +52,7 @@ jobs:
 
   jwt-2:
     name: Authentication with jwt ${{ matrix.jwt }} (Ruby 3.1)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     timeout-minutes: 15
     strategy:
       fail-fast: false