diff --git a/TurTLE/tools.py b/TurTLE/tools.py
index 82bcaf6c48072592e0f0dbefe0a057db2a7f1309..7ddbf32d2e6d0beee57d11db75c5b07dbd0e5f86 100644
--- a/TurTLE/tools.py
+++ b/TurTLE/tools.py
@@ -407,7 +407,7 @@ def distribute_cores_evenly(
     for t in range(nthreads_per_process):
         single_process_mask[t*skip] = 1
 
-    single_process_mask = sum(single_process_mask[i]*(2**i) for i in range(max_cores_per_process))
+    single_process_mask = sum(int(single_process_mask[i])*(2**i) for i in range(max_cores_per_process))
 
     # now create full node mask:
     all_masks = []