diff --git a/snapshot b/snapshot
index cfff51a..455d41f 100755
--- a/snapshot
+++ b/snapshot
@@ -166,11 +166,11 @@
       thread.start()
 
   def get_filename(self):
-    if self.oneshot:
-      filename = self.prefix + '.' + self.suffix
-    else:
+    while True:
       filename = self.prefix + str(self.num).zfill(4) + '.' + self.suffix
       self.num = self.num + 1
+      if not os.path.exists(filename):
+        break
 
     return filename