diff --git a/content/assignments/parallel-firewall/tests/Makefile b/content/assignments/parallel-firewall/tests/Makefile
index 9594203177..c0e84c6022 100644
--- a/content/assignments/parallel-firewall/tests/Makefile
+++ b/content/assignments/parallel-firewall/tests/Makefile
@@ -6,10 +6,10 @@ UTILS_PATH = $(realpath ../utils)
 all: src
 
 src:
-	make -C $(SRC_PATH) UTILS_PATH=$(UTILS_PATH)
+	$(MAKE) -C $(SRC_PATH) UTILS_PATH=$(UTILS_PATH)
 
 check: clean
-	make -i SRC_PATH=$(SRC_PATH)
+	-$(MAKE) SRC_PATH=$(SRC_PATH)
 	SRC_PATH=$(SRC_PATH) python3 checker.py
 
 lint:
@@ -20,7 +20,7 @@ lint:
 	# -cd $(SRC_PATH)/.. && pylint tests/*.py
 
 clean:
-	make -C $(SRC_PATH) clean
+	$(MAKE) -C $(SRC_PATH) clean
 	-rm -f *~
 	-rm -rf __pycache__
 	-rm -rf out
diff --git a/content/assignments/parallel-firewall/tests/checker.py b/content/assignments/parallel-firewall/tests/checker.py
index 541b1f85dc..ef099af05b 100644
--- a/content/assignments/parallel-firewall/tests/checker.py
+++ b/content/assignments/parallel-firewall/tests/checker.py
@@ -175,6 +175,10 @@ def run_once_and_check_output(
     except FileNotFoundError:
         pass
 
+    if not os.path.exists(binary):
+        print("No program to run, maybe compilation failed?")
+        return False
+
     with subprocess.Popen(
         [binary, in_file_path, out_file_path, f"{threads}"],
         stdout=subprocess.PIPE,