diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index f291a86..25510ba 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -22,6 +22,19 @@ jobs:
         with:
           enable-cache: true
 
+      # A release tag whose version was never bumped in pyproject.toml only
+      # surfaces at upload time, as an opaque PyPI "400 File already exists".
+      # Fail here instead, before the tests even run.
+      - name: Check the release tag matches the package version
+        if: github.event_name == 'release'
+        run: |
+          tag="${GITHUB_REF_NAME#v}"
+          packaged="$(uv version --short)"
+          if [ "$tag" != "$packaged" ]; then
+            echo "::error::Release tag v$tag does not match pyproject.toml version $packaged — bump the version, merge, then re-tag."
+            exit 1
+          fi
+
       - name: Test (gate the release)
         run: uv run --group dev pytest -q
 
diff --git a/pyproject.toml b/pyproject.toml
index 12d35bf..b6e7f3c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "lokf"
-version = "0.2.0"
+version = "0.3.0"
 description = "Linked Open Knowledge Format (LOKF) — a semantic profile of Google's Open Knowledge Format, defined once in LinkML"
 readme = "README.md"
 license = "CC-BY-4.0"
diff --git a/uv.lock b/uv.lock
index c049c52..3d85c8e 100644
--- a/uv.lock
+++ b/uv.lock
@@ -833,7 +833,7 @@ wheels = [
 
 [[package]]
 name = "lokf"
-version = "0.2.0"
+version = "0.3.0"
 source = { editable = "." }
 dependencies = [
     { name = "linkml-runtime" },