diff --git a/jass_preprocessing/__main__.py b/jass_preprocessing/__main__.py
index 2081c6810096fc43d93e5f79b255105650a843c5..ad6d58d46116db8e02b040d91d65d788a8347c24 100644
--- a/jass_preprocessing/__main__.py
+++ b/jass_preprocessing/__main__.py
@@ -61,7 +61,7 @@ def launch_preprocessing(args):
         mgwas = jp.map_reference.map_on_ref_panel(gw_df, ref, gwas_map.loc[tag, "index_type"])
         mgwas = jp.map_reference.compute_snp_alignement(mgwas)
         mgwas = jp.compute_score.compute_z_score(mgwas)
-        mgwas = jp.compute_score.compute_sample_size(mgwas, args.diagnostic_folder, tag, args.percent_sample_size)
+        mgwas = jp.compute_score.compute_sample_size(mgwas, args.diagnostic_folder, tag, float(args.percent_sample_size))
         end = time.time()
 
         print("Preprocessing of {0} in {1}s".format(tag, end-start))