diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index a011d8d0f9..826f2f5d3a 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -298,7 +298,7 @@ jobs:
         path: build
     - name: Test
       shell: bash
-      run: ci/run-test-slice-meson.sh build ${{matrix.nr}} 10
+      run: ci/run-test-slice-meson.sh build $((${{matrix.nr}} + 1)) 10
     - name: print test failures
       if: failure() && env.FAILED_TEST_ARTIFACTS != ''
       shell: bash
diff --git a/ci/run-test-slice-meson.sh b/ci/run-test-slice-meson.sh
index 961c94fba0..a6df927ba5 100755
--- a/ci/run-test-slice-meson.sh
+++ b/ci/run-test-slice-meson.sh
@@ -9,5 +9,5 @@
 
 group "Run tests" \
 	meson test -C "$1" --no-rebuild --print-errorlogs \
-		--test-args="$GIT_TEST_OPTS" --slice "$((1+$2))/$3" ||
+		--test-args="$GIT_TEST_OPTS" --slice "$(($2))/$3" ||
 handle_failed_tests