diff --git a/data-validation.js b/data-validation.js
index 37ea0db..47d8906 100644
--- a/data-validation.js
+++ b/data-validation.js
@@ -202,7 +202,7 @@ function validateRs(rs, bik, error) {
 			var checksum = 0;
 			var coefficients = [7, 1, 3, 7, 1, 3, 7, 1, 3, 7, 1, 3, 7, 1, 3, 7, 1, 3, 7, 1, 3, 7, 1];
 			for (var i in coefficients) {
-				checksum += coefficients[i] * (bikRs[i] % 10);
+				checksum += (coefficients[i] * bikRs[i] % 10);
 			}
 			if (checksum % 10 === 0) {
 				result = true;
@@ -253,4 +253,4 @@ function validateSnils(snils, error) {
 		}
 	}
 	return result;
-}
\ No newline at end of file
+}