Fixes
diff --git a/gds_to_lef_gds_mag.py b/gds_to_lef_gds_mag.py
index 3a2cf31..2adc8a6 100755
--- a/gds_to_lef_gds_mag.py
+++ b/gds_to_lef_gds_mag.py
@@ -864,11 +864,10 @@
     with open(mag_in_file, 'r') as f:
         contents = f.read()
 
-    mag_base = os.path.basename(mag_out_file)
-    gds_base = mag_base.replace('.mag', '.gds')
-
     contents = re.sub('timestamp [0-9]+', 'timestamp 0', contents)
-    contents = re.sub('string GDS_FILE .*', 'string GDS_FILE '+gds_base, contents)
+    def basename(m):
+        return 'string GDS_FILE '+os.path.basename(m.group(1))
+    contents = re.sub('string GDS_FILE (.*)', basename, contents)
 
     with open(mag_out_file, 'w') as f:
         f.write(contents)