diff --git a/.github/workflows/apko-smoke-test.yaml b/.github/workflows/apko-smoke-test.yaml
index 056e8a2..f6a6860 100644
--- a/.github/workflows/apko-smoke-test.yaml
+++ b/.github/workflows/apko-smoke-test.yaml
@@ -78,6 +78,23 @@ jobs:
           EXPECTED_VERSION: ${{ inputs.expected-version }}
         run: |
           set -euo pipefail
+          # Fetch the image up front so a runner that cannot run it fails here.
+          # Inside the loop below docker's own errors (no daemon, image absent)
+          # are captured as command output and only a narrow set of exit codes
+          # is fatal, so they would otherwise pass as a test that never ran.
+          docker pull --platform "linux/$IMAGE_ARCH" "$IMAGE"
+
+          # `docker pull --platform` is happy to fetch a foreign arch, which
+          # then fails at `docker run` with an exit code the loop tolerates. No
+          # binfmt/qemu is registered on stock runners, so a smoke runner whose
+          # arch does not match the image can only produce a test that skips
+          # the image while reporting success.
+          pulled_arch="$(docker image inspect --format '{{.Architecture}}' "$IMAGE")"
+          if [ "$pulled_arch" != "$IMAGE_ARCH" ]; then
+            echo "FAIL: $IMAGE is $pulled_arch but this runner is $IMAGE_ARCH; the image cannot execute here" >&2
+            exit 1
+          fi
+
           version_matched=false
           normalized_version="${EXPECTED_VERSION#v}"
           IFS=',' read -ra tests <<< "$SMOKE_TEST"
diff --git a/actions/apko-plan/apko-plan.sh b/actions/apko-plan/apko-plan.sh
index 9a70c04..50bc5dd 100755
--- a/actions/apko-plan/apko-plan.sh
+++ b/actions/apko-plan/apko-plan.sh
@@ -72,8 +72,10 @@ emit_outputs() {
   has_builds=$( [[ $(echo "$apko_matrix" | jq 'length') -gt 0 ]] && echo true || echo false )
   smoke_matrix=$(echo "$apko_matrix" | jq -c --slurpfile config "$CONFIG" '
     def trim: sub("^\\s+"; "") | sub("\\s+$"; "");
+    # Both defaults must provide a docker daemon: the smoke test runs the
+    # published image, and a runner without one turns the test into a no-op.
     def smoke_runner($smoke_runners; $arch):
-      ($smoke_runners[$arch] // (if $arch == "arm64" then "ubuntu-24.04-arm" else "ubuntu-slim" end));
+      ($smoke_runners[$arch] // (if $arch == "arm64" then "ubuntu-24.04-arm" else "ubuntu-24.04" end));
     ($config[0].smoke_runners // {}) as $smoke_runners
     | [.[] | select((.smoke_test // "") != "")
       | . as $image
diff --git a/actions/apko-plan/apko-plan.test.sh b/actions/apko-plan/apko-plan.test.sh
index 34586bb..e937191 100755
--- a/actions/apko-plan/apko-plan.test.sh
+++ b/actions/apko-plan/apko-plan.test.sh
@@ -116,4 +116,39 @@ assert_json "$variant_apko" '[.[] | select(.tag_suffix == "-dev")][0].smoke_test
 assert_json "$variant_melange" 'length' '1'
 assert_json "$variant_smoke" 'length' '1'
 
+# The default smoke runner must be able to run the built image. A runner
+# without a docker daemon does not fail the job: `docker run` writes its error
+# to the captured output and the loop only rejects a narrow set of exit codes,
+# so every smoke test silently passes without the image ever starting.
+default_runner_config="$TEST_DIR/default-runners.json"
+jq 'del(.smoke_runners) | .apko_archs = "amd64,arm64"' "$CONFIG" > "$default_runner_config"
+
+default_runner_output="$TEST_DIR/default-runners.out"
+GITHUB_EVENT_NAME=workflow_dispatch \
+GITHUB_REF_TYPE=branch \
+GITHUB_REF_NAME=main \
+GITHUB_OUTPUT="$default_runner_output" \
+  "$SCRIPT_DIR/apko-plan.sh" "$default_runner_config"
+
+default_runner_smoke=$(output_value "$default_runner_output" smoke_matrix_json)
+assert_json "$default_runner_smoke" '[.[] | select(.arch == "amd64")][0].runner' 'ubuntu-24.04'
+assert_json "$default_runner_smoke" '[.[] | select(.arch == "arm64")][0].runner' 'ubuntu-24.04-arm'
+
+# An explicit smoke_runners entry still wins over the default, and an arch the
+# override omits falls back to the default rather than to the overridden value.
+partial_override_config="$TEST_DIR/partial-override.json"
+jq '.smoke_runners = {"amd64": "ubuntu-latest"} | .apko_archs = "amd64,arm64"' \
+  "$CONFIG" > "$partial_override_config"
+
+partial_override_output="$TEST_DIR/partial-override.out"
+GITHUB_EVENT_NAME=workflow_dispatch \
+GITHUB_REF_TYPE=branch \
+GITHUB_REF_NAME=main \
+GITHUB_OUTPUT="$partial_override_output" \
+  "$SCRIPT_DIR/apko-plan.sh" "$partial_override_config"
+
+partial_override_smoke=$(output_value "$partial_override_output" smoke_matrix_json)
+assert_json "$partial_override_smoke" '[.[] | select(.arch == "amd64")][0].runner' 'ubuntu-latest'
+assert_json "$partial_override_smoke" '[.[] | select(.arch == "arm64")][0].runner' 'ubuntu-24.04-arm'
+
 echo "apko-plan tests passed"