diff --git a/flow/util/addDummyToLef.py b/flow/util/addDummyToLef.py
index 3c0c828eec..2dc433f40e 100755
--- a/flow/util/addDummyToLef.py
+++ b/flow/util/addDummyToLef.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+import os
 import re
 import sys
 import argparse  # argument parsing
@@ -14,9 +15,12 @@
 args = parser.parse_args()
 
 
-f = open(args.inputLef)
-content = f.read()
-f.close()
+if not os.path.isfile(args.inputLef):
+    print(f"Error: Input LEF not found: {args.inputLef}", file=sys.stderr)
+    sys.exit(1)
+
+with open(args.inputLef) as f:
+    content = f.read()
 
 # refMacro = "BUFH_X1M_A12TR"
 
@@ -26,9 +30,8 @@
 result, count = re.subn(pattern, replace, content, 1, re.S)
 
 if count > 0:
-    f = open(args.outputLef, "w")
-    f.write(result)
-    f.close()
+    with open(args.outputLef, "w") as f:
+        f.write(result)
 else:
-    print("Error: Pattern not found")
+    print("Error: Pattern not found", file=sys.stderr)
     sys.exit(1)