diff --git a/raiss/ld_matrix.py b/raiss/ld_matrix.py
index 982e1417f06feff03b4178f086284a21a047dabf..8e33cc075a61eb0743ce864473d4bb983bbbd618 100644
--- a/raiss/ld_matrix.py
+++ b/raiss/ld_matrix.py
@@ -117,7 +117,7 @@ def generate_genome_matrices(region_files, reffolder, folder_output, prefix, suf
         prefix (str): part of file name in reffolder before the chromosome number
         suffix (str): part of file name in reffolder after the chromosome number (without extension)
     """
-    regions = pd.read_csv(region_files,sep=separa)
+    regions = pd.read_csv(region_files,sep=separa, dtype={'chr':str, 'start':np.int64, 'stop':np.int64})
 
     for reg in regions.iterrows():
         # input reference panel file