diff --git a/suite2p/registration/zalign.py b/suite2p/registration/zalign.py
index 67d8851d..d0beca80 100644
--- a/suite2p/registration/zalign.py
+++ b/suite2p/registration/zalign.py
@@ -157,10 +157,10 @@ def compute_zpos(Zreg, ops, reg_file=None):
         ]
 
     reg_file = ops["reg_file"] if reg_file is None else reg_file
-    nbytes = os.path.getsize(ops["reg_file"])
+    nbytes = os.path.getsize(reg_file)
     nFrames = int(nbytes / (2 * Ly * Lx))
 
-    reg_file = open(ops["reg_file"], "rb")
+    reg_file = open(reg_file, "rb")
     refAndMasks = []
     for Z in Zreg:
         if ops["1Preg"]: