diff --git a/Koha/Patrons/Import.pm b/Koha/Patrons/Import.pm
index fe63b9567e..d98e44d7c5 100644
--- a/Koha/Patrons/Import.pm
+++ b/Koha/Patrons/Import.pm
@@ -132,6 +132,7 @@ sub import_patrons {
                 }
             }
         }
+        $borrower{cardnumber} = undef unless $borrower{cardnumber};
 
         # Check if borrower category code exists and if it matches to a known category. Pushing error to missing_criticals otherwise.
         $self->check_borrower_category($borrower{categorycode}, $borrowerline, $line_number, \@missing_criticals);