diff --git a/jass/models/inittable.py b/jass/models/inittable.py
index 0ae5d9615644f7948360c5e5fe0e463d73c47d9c..bf1573992b30460f4da749c4324a0cd557454c92 100644
--- a/jass/models/inittable.py
+++ b/jass/models/inittable.py
@@ -186,8 +186,8 @@ def compute_covariance_zscore(init_file_path, path_covariance=None):
     NSNP_matrix = DataFrame(index=trait, columns=trait)
     cov_matrix = DataFrame(index=trait, columns=trait)
 
-    cov_matrix.fillna(0, inplace=True)
-    NSNP_matrix.fillna(0, inplace=True)
+    cov_matrix.fillna(0.0, inplace=True)
+    NSNP_matrix.fillna(0.0, inplace=True)
     Regions = read_hdf(
         init_file_path,
         "Regions")