diff --git a/useful_scripts/conc_gzip_files.py b/useful_scripts/conc_gzip_files.py
index 340c68f..ce83445 100644
--- a/useful_scripts/conc_gzip_files.py
+++ b/useful_scripts/conc_gzip_files.py
@@ -17,7 +17,7 @@ def conc_gzip_files(in_dir, out_file, append=False):
     write_mode = 'w'
     if append:
         write_mode = 'a'
-    gzips = [os.path.join(in_dir, i) for i in os.listdir(in_dir) if i.endswith(i)]
+    gzips = [os.path.join(in_dir, i) for i in os.listdir(in_dir) if i.endswith('.gz')]
     with open(out_file, write_mode) as ofile:
         for f in gzips:
             with gzip.open(f, 'rb') as gzipf: