diff --git a/src/math/big/prime.go b/src/math/big/prime.go
index 4c2c152f65e..d9a5f1ec968 100644
--- a/src/math/big/prime.go
+++ b/src/math/big/prime.go
@@ -51,7 +51,7 @@ func (x *Int) ProbablyPrime(n int) bool {
 	}
 
 	if w&1 == 0 {
-		return false // n is even
+		return false // x is even
 	}
 
 	const primesA = 3 * 5 * 7 * 11 * 13 * 17 * 19 * 23 * 37