diff --git a/calc_gate.c b/calc_gate.c
index cfe9890..f410d4a 100644
--- a/calc_gate.c
+++ b/calc_gate.c
@@ -83,7 +83,7 @@ int data_validity_check(struct param_gate *param)
 	if(param->wingwall >=warped_wingwall || param->wingwall<=parallel_wingwall){
 		return -1;
 	}
-	if(!(param->drop_step = 0 || param->drop_step =1)){
+	if(!(param->drop_step == 0 || param->drop_step == 1)){
 		return -1;
 	}
 	if(param->openning_height_of_gate <-0.0000001){