diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 25aafba..9b26d96 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,6 +38,15 @@ jobs:
       - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v30
       - uses: ./
+      - name: Make the nix command fail
+        uses: ./
+        with:
+          arguments: --a-bad-flag
+        id: should-fail
+        continue-on-error: true
+      - name: Fail if the action succeeded when the nix command failed
+        if: steps.should-fail.outcome == 'success'
+        run: exit 1
   check:
     strategy:
       matrix:
diff --git a/nix-develop-gha.sh b/nix-develop-gha.sh
index eaaea0a..3c18193 100755
--- a/nix-develop-gha.sh
+++ b/nix-develop-gha.sh
@@ -12,7 +12,8 @@ contains() {
 envOutput=
 
 # Iterate over the output of `env -0` in the shell environment
-while IFS='=' read -r -d '' n v; do
+while IFS='=' read -r -d '' n v || exit "$n"
+do
 	# If this variable is empty then we're in the first loop, and $n is the
 	# output of the shellHook _before_ `env` is run.
 	if ! [ "$envOutput" ]; then
@@ -68,4 +69,4 @@ while IFS='=' read -r -d '' n v; do
 	fi
 	# Add all environment variables except for PATH to GITHUB_ENV.
 	printf "%s=%s\n" "$n" "$v" >>"${GITHUB_ENV:-/dev/stderr}"
-done < <(nix develop "${arguments[@]}" --command bash -c "echo -ne '\0'; env -0")
+done < <(set +e; nix develop "${arguments[@]}" --command bash -c "echo -ne '\0'; env -0"; printf '%s' "$?")