diff --git a/.github/workflows/release-client.yml b/.github/workflows/release-client.yml
index ff28ac51..cb645bee 100644
--- a/.github/workflows/release-client.yml
+++ b/.github/workflows/release-client.yml
@@ -36,6 +36,19 @@ jobs:
         with:
           version: '0.8.2'
 
+      - name: Validate version number
+        env:
+          VERSION: ${{ github.event.inputs.version }}
+        run: |
+          MAJOR=$(echo "$VERSION" | cut -d. -f1)
+          if [ "$MAJOR" -ge 26 ]; then
+            echo "Error: Version $VERSION is not allowed. Major version must be below 26."
+            echo ""
+            echo "This is likely not the version you want to release, it looks like calver."
+            echo "See README.md for more information about versioning."
+            exit 1
+          fi
+
       - name: Prepare release
         uses: getsentry/craft@c6e2f04939b6ee67030588afbb5af76b127d8203 # v2
         env:
diff --git a/README.md b/README.md
index 7a4f79bc..a47076fb 100644
--- a/README.md
+++ b/README.md
@@ -101,6 +101,12 @@ See the [python client README](./clients/python/README.md) for more information.
 
 ### Releasing clients
 
+**Note:** Clients are separately released from the broker. The broker follows
+self-hosted style calver releases (`26.4.0`), and clients are released using
+regular semver (`0.1.8`). They share tags and release branches though, so the
+latest release you see on GitHub may not be the one you have to base your
+version number on.
+
 1. Use the [release client libraries workflow](https://github.com/getsentry/taskbroker/actions/workflows/release-client.yml)
 2. Choose 'Run workflow' and enter a version number in.
 3. This will use craft + getsentry/publish to add packages to both internal and public pypi.