diff --git a/prosopopee/prosopopee.py b/prosopopee/prosopopee.py
index 7d4a75c..33d6aa6 100644
--- a/prosopopee/prosopopee.py
+++ b/prosopopee/prosopopee.py
@@ -91,9 +91,7 @@ class Video(object):
         return ""
 
     def generate_thumbnail(self, gm_geometry):
-        thumbnail_name = self.name.split(".")
-        thumbnail_name[-2] += "-%s" % gm_geometry
-        thumbnail_name = thumbnail_name[-2] + ".png"
+        thumbnail_name = ".".join(self.name.split(".")[:-1] + ["-", gm_geometry, ".png"])
 
         source, target = os.path.join(self.base_dir, self.name), os.path.join(self.target_dir, thumbnail_name)