diff --git a/requirements.txt b/requirements.txt
index 38c2083..ee07df1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,3 @@
-yaml
+PyYaml
 praw
-optparse
 zipfile
\ No newline at end of file
diff --git a/riddle.py b/riddle.py
index 87adce3..df67e5f 100644
--- a/riddle.py
+++ b/riddle.py
@@ -169,6 +169,22 @@ def download_images(images: list, dl_dir: str):
           (realcount, imgcount, dl_dir, preexist))
 
 
+def filter_zip_files(images: list, zip_fname: str):
+    """
+    Removes the images that already exist in the zip-file
+    :param images:
+    :param zip_fname:
+    :return:
+    """
+    if os.path.isfile(zip_fname):
+        zfile = zipfile.ZipFile(zip_fname, 'r')
+        zfnames = [f.filename for f in zfile.infolist()]
+        print('[~] Removing entries already in zip-file')
+        return [img for img in images if img.split('/')[-1] not in zfnames]
+    else:
+        return images
+
+
 def compress_folder(folder: str, zip_fname: str):
     """
     Zips the contents of a folder to the destination zipfile name.
@@ -221,9 +237,10 @@ def main():
                 dldest = options.output  # uses the -o output destination
             images = get_images(client, subreddit, limit=options.count,
                                 nsfw=options.nsfw)
-            if options.zip:  # download to zip instead
-                download_images(images, '.cache')  # download to cache
-                compress_folder('.cache', dldest + '.zip')  # add to zip
+            if options.zip:  # downloads to a cache-folder first before compressing it to zip
+                images = filter_zip_files(images, dldest+'.zip')
+                download_images(images, '.cache')
+                compress_folder('.cache', dldest+'.zip')
                 shutil.rmtree('.cache')
             else:
                 download_images(images, dldest)
diff --git a/test.zip b/test.zip
new file mode 100644
index 0000000..3458a09
Binary files /dev/null and b/test.zip differ