diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9be7899..d034dd9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,6 +13,17 @@ env:
   SBT_OPTS: "-Xmx4G -XX:+UseG1GC"
 
 jobs:
+  version:
+    name: Check the version bump
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Fail unless build.sbt bumps the version
+        run: ./scripts/check-version-bump
+
   native:
     name: Native library (${{ matrix.platform }})
     runs-on: ${{ matrix.runner }}
diff --git a/README.md b/README.md
index 73a5ab7..afa2316 100644
--- a/README.md
+++ b/README.md
@@ -75,7 +75,8 @@ On a push to `main` that job publishes the jar to GitHub Packages.
 That jar has no classifier.
 At runtime sbt-jni reads `uname -sm` and loads the library from the directory with that name.
 
-GitHub Packages rejects a second publish of the same version, so bump `ThisBuild / version` in `build.sbt` for every PR that changes the library.
+GitHub Packages rejects a second publish of the same version, so bump `ThisBuild / version` in `build.sbt` in every PR.
+A CI job on each PR runs `scripts/check-version-bump` and fails when the version matches main.
 
 ### Troubleshooting
 
diff --git a/build.sbt b/build.sbt
index b8cca47..7b55363 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,7 +1,7 @@
 import Dependencies._
 
 ThisBuild / scalaVersion       := "2.13.15"
-ThisBuild / version            := "0.0.15"
+ThisBuild / version            := "0.0.16"
 ThisBuild / versionScheme      := Some("early-semver")
 ThisBuild / organization       := "io.citrine"
 ThisBuild / organizationName   := "Citrine Informatics"
diff --git a/scripts/check-version-bump b/scripts/check-version-bump
new file mode 100755
index 0000000..994176f
--- /dev/null
+++ b/scripts/check-version-bump
@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Fail unless build.sbt sets a version that differs from the one on main.
+# GitHub Packages rejects a second publish of the same version, so every merge must bump it.
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+git fetch --quiet origin main:refs/remotes/origin_main
+
+extract_version() {
+  grep -E '^ThisBuild / version +:=' | sed -nE 's/.*"([^"]+)".*/\1/p'
+}
+
+head_version=$(extract_version < build.sbt)
+main_version=$(git cat-file blob origin_main:build.sbt | extract_version)
+
+if [[ "$head_version" == "$main_version" ]]; then
+  echo "build.sbt still sets version $main_version, the version on main. Bump it before merging." >&2
+  exit 1
+fi
+
+echo "Version bumps from $main_version to $head_version"