diff --git a/.github/workflows/benchmarks.yaml b/.github/workflows/benchmarks.yaml
index df3e10e..e83b35f 100644
--- a/.github/workflows/benchmarks.yaml
+++ b/.github/workflows/benchmarks.yaml
@@ -42,19 +42,25 @@ jobs:
           enable-cache: true
 
       - name: Benchmark head
-        run: >
-          uv run --with "$BENCHMEM" pytest benchmarks/ $BENCH_ARGS
-          --benchmark-json "$RUNNER_TEMP/head.json"
+        run: |
+          uv run --with "$BENCHMEM" pytest benchmarks/ $BENCH_ARGS \
+            --benchmark-json "$RUNNER_TEMP/head.json"
+          uv run --no-sync python -c "import tsam; print('head tsam:', tsam.__version__)"
 
       - name: Benchmark base (${{ github.event.pull_request.base.ref }})
         if: github.event_name == 'pull_request'
         # Base src with the head's benchmark suite overlaid, so test IDs match
         # and suite edits in the PR still compare against the same cases.
+        # Drop the head run's uv.lock (untracked — the repo commits none):
+        # uv keeps a satisfying lock as-is, so without this a head that
+        # changes dependencies leaks its resolution into the base run.
         run: |
           git checkout --detach ${{ github.event.pull_request.base.sha }}
           git checkout ${{ github.sha }} -- benchmarks/
+          rm -f uv.lock
           uv run --with "$BENCHMEM" pytest benchmarks/ $BENCH_ARGS \
             --benchmark-json "$RUNNER_TEMP/base.json"
+          uv run --no-sync python -c "import tsam; print('base tsam:', tsam.__version__)"
 
       - name: Render report and plot
         run: |
diff --git a/pyproject.toml b/pyproject.toml
index b308d56..19472e3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -84,3 +84,6 @@ exclude_lines = [
 [tool.pytest.ini_options]
 testpaths = ["test"]
 addopts = ["-n", "auto", "--dist", "loadfile"]
+
+[tool.uv.sources]
+tsam = { git = "https://github.com/FZJ-IEK3-VSA/tsam", branch = "develop-v4" }