diff --git a/modules/math.js b/modules/math.js
index db1d21b..0294f8e 100644
--- a/modules/math.js
+++ b/modules/math.js
@@ -164,6 +164,11 @@ function modsqrt(n, modulus) {
 	}
 
 	// TODO: add special case for modulus = 3 (mod 4)
+	
+	n %= modulus;
+	if (n < 0n) {
+		n += modulus;
+	}
 
 	if (n % modulus === 0n) {
 		return 0n;