diff --git a/python_package/src/onlinemid/roi/roi.py b/python_package/src/onlinemid/roi/roi.py
index e19ba726bbc4e9c6d52baead880bcd58cc77bcfd..6d1df5a74ad88af5b58769dd43fdbf6671a1cd44 100644
--- a/python_package/src/onlinemid/roi/roi.py
+++ b/python_package/src/onlinemid/roi/roi.py
@@ -27,8 +27,9 @@ def make_onlineroi_from_roi_array(roi_array):
 
             if val == True:
                 length = 1
-                while roi_ravel[index+length] == True:
-                    length +=1         
+                if index+length < roi_array.size:
+                    while roi_ravel[index+length] == True:
+                        length +=1         
 
                 print("(index, lnegth)", index, length)
                 compressed_data.add(np.array([index, length], dtype=np.uint64))