diff --git a/src/bayesvalidrox/bayes_inference/bayes_inference.py b/src/bayesvalidrox/bayes_inference/bayes_inference.py
index a816e2348c2d5c0c37c5c8e3f376e2a4917ba895..2c4d9b3abcf6491dd586ff5348149725ec981f3e 100644
--- a/src/bayesvalidrox/bayes_inference/bayes_inference.py
+++ b/src/bayesvalidrox/bayes_inference/bayes_inference.py
@@ -346,7 +346,7 @@ class BayesInference:
 
                 # Prepare data dataframe
                 nobs = list(self.measured_data.count().values[1:])
-                numbers = list(map(sum, zip([0] + nobs, nobs)))
+                numbers = list(np.cumsum(nobs))
                 indices = list(zip([0] + numbers, numbers))
                 data_dict = {
                     output_names[i]: data[j:k] for i, (j, k) in