diff --git a/.github/workflows/binaries-linux-x64.yml b/.github/workflows/binaries-linux-x64.yml
index 1d438fa93..e082d0a75 100644
--- a/.github/workflows/binaries-linux-x64.yml
+++ b/.github/workflows/binaries-linux-x64.yml
@@ -14,6 +14,10 @@ jobs:
       # image: https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2404-Readme.md
     container: alpine:latest
 
+    env:
+      stack: stack
+      ghc:   9.10.1
+
     steps:
 
     - name: Check out
diff --git a/.github/workflows/binaries-mac-arm64.yml b/.github/workflows/binaries-mac-arm64.yml
index d94bd2587..e32fe9e12 100644
--- a/.github/workflows/binaries-mac-arm64.yml
+++ b/.github/workflows/binaries-mac-arm64.yml
@@ -6,6 +6,7 @@ on:
   push:
     branches: [ binaries-mac-arm64, binaries ]
   workflow_dispatch:
+
 jobs:
   build:
     runs-on: macos-14
@@ -13,8 +14,8 @@ jobs:
       # image: https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md
 
     env:
-      ghc: 9.12.2
       stack: stack
+      ghc:   9.10.1
 
     steps:
 
diff --git a/.github/workflows/binaries-mac-x64.yml b/.github/workflows/binaries-mac-x64.yml
index 07554ae7f..a04e79472 100644
--- a/.github/workflows/binaries-mac-x64.yml
+++ b/.github/workflows/binaries-mac-x64.yml
@@ -6,6 +6,7 @@ on:
   push:
     branches: [ binaries-mac-x64, binaries ]
   workflow_dispatch:
+
 jobs:
   build:
     runs-on: macos-13
@@ -14,6 +15,8 @@ jobs:
 
     env:
       stack: stack
+      ghc:   9.10.1
+
     steps:
 
     - name: Show platform info
diff --git a/.github/workflows/binaries-windows-x64.yml b/.github/workflows/binaries-windows-x64.yml
index d9b395e88..62e3f15f7 100644
--- a/.github/workflows/binaries-windows-x64.yml
+++ b/.github/workflows/binaries-windows-x64.yml
@@ -6,6 +6,7 @@ on:
   push:
     branches: [ binaries-windows-x64, binaries ]
   workflow_dispatch:
+
 jobs:
   build:
     runs-on: windows-latest
@@ -19,6 +20,7 @@ jobs:
     env:
       # use preinstalled ghc 9.12.2
       stack: stack --system-ghc --no-install-ghc --stack-yaml stack912.yaml
+      ghc:   9.12.2
 
     steps:
 
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3e87b94a1..fb6d7dc1d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -50,11 +50,8 @@ jobs:
       # image: https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2404-Readme.md
 
     env:
-      # caching id for this ghc's build artifacts
-      ghc: 910
-
-      # select the right stack yaml for this ghc
       stack: stack
+      ghc:   9.10.1
 
       # flag for skipping later steps, declared here to prevent "Context access might be invalid" warnings
       do-all:
diff --git a/.github/workflows/oldest.yml b/.github/workflows/oldest.yml
index 2f9dce8be..cab7e84d9 100644
--- a/.github/workflows/oldest.yml
+++ b/.github/workflows/oldest.yml
@@ -17,14 +17,8 @@ jobs:
       # image: https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2404-Readme.md
 
     env:
-      # This workflow uses github's preinstalled ghc & stack on ubuntu.
-      # Keep these synced with the latest ghc version at https://github.com/actions/runner-images/blob/ubuntu22/20240514.2/images/ubuntu/Ubuntu2404-Readme.md#haskell-tools
-      #
-      # caching id for this ghc's build artifacts:
-      # XXX supposed to be interpolated by $ghc below, but this is not working
-      ghc: 8107
-      # stack config for this ghc:
       stack: stack --stack-yaml=stack810.yaml
+      ghc:   8.10.7
 
     steps: