diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index f603f09..233ff35 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -83,6 +83,7 @@ jobs:
           fi
 
       - name: Ensure test image is available (${{ matrix.arch_name }})
+        id: ensure-test-image
         run: |
           bash "${{ matrix.test_script }}" load
 
@@ -91,7 +92,7 @@ jobs:
           bash "${{ matrix.test_script }}" run -vv test
 
       - name: Save test image to cache path (${{ matrix.arch_name }})
-        if: always()
+        if: ${{ !cancelled() && steps.ensure-test-image.outcome == 'success' }}
         run: |
           docker image inspect "${{ matrix.image_name }}" >/dev/null 2>&1
           docker save "${{ matrix.image_name }}" -o "${{ matrix.image_tar }}"
diff --git a/etc/linux-container.Dockerfile b/etc/linux-container.Dockerfile
index f73743f..7e6ca62 100644
--- a/etc/linux-container.Dockerfile
+++ b/etc/linux-container.Dockerfile
@@ -13,8 +13,11 @@ RUN python -m pip install -U --no-cache-dir pip
 RUN NINJAFLAGS='-v' python -m pip install -v --no-cache-dir \
     "numpy<2"
 
-RUN NINJAFLAGS='-v' python -m pip install -v --no-build-isolation --no-deps --no-cache-dir \
-    ml_dtypes
+# Build against the installed NumPy 1.x on 32-bit platforms. ml_dtypes 0.6
+# requires NumPy 2 and uses a different build backend.
+RUN python -m pip install --no-cache-dir "setuptools~=80.9.0" \
+    && NINJAFLAGS='-v' python -m pip install -v --no-build-isolation --no-deps --no-cache-dir \
+    "ml_dtypes==0.5.4"
 
 RUN NINJAFLAGS='-v' python -m pip install -v --no-cache-dir \
     psutil \