diff --git a/jass_preprocessing/map_reference.py b/jass_preprocessing/map_reference.py
index 1949b1bbcfdbcea27b5f43ba43167aa91e484ff9..2b676aa5d141b3e4cc2fc4463af1fb4a208267ca 100644
--- a/jass_preprocessing/map_reference.py
+++ b/jass_preprocessing/map_reference.py
@@ -83,7 +83,7 @@ def map_on_ref_panel(gw_df , ref_panel, index_type="rs-number"):
             raise ValueError("index_type can take only two values: 'rs-number' or 'positional'")
 
     if (("pos" in merge_GWAS.columns) and ("POS" in merge_GWAS.columns)):
-        if (merge_GWAS.pos == merge_GWAS.POS).mean()> 0.95):
+        if ((merge_GWAS.pos == merge_GWAS.POS).mean()> 0.95):
             merge_GWAS = merge_GWAS.loc[(merge_GWAS.pos == merge_GWAS.POS)]
         else:
             raise ValueError("SNP positions in reference panel and in Summary statistic are different! Different assembly?")