diff --git a/tests/blif/generate_mk.py b/tests/blif/generate_mk.py
index 41f2d769d..47cb9accd 100644
--- a/tests/blif/generate_mk.py
+++ b/tests/blif/generate_mk.py
@@ -6,6 +6,6 @@ sys.path.append("..")
 import gen_tests_makefile
 
 gen_tests_makefile.generate(["--yosys-scripts"], [],
-"""if [ -f $(@:.ys=.blif) ]; then \\
-    diff <(tail -n +2 $(@:.ys=.blif).out) <(tail -n +2 $(@:.ys=.blif).ok) >/dev/null 2>&1; \\
-fi""")
\ No newline at end of file
+"""[ ! -f $(@:.ys=.blif) ] || \\
+    diff <(tail -n +2 $(@:.ys=.blif).out) <(tail -n +2 $(@:.ys=.blif).ok) >/dev/null 2>&1 || exit 1; \\
+""")
\ No newline at end of file