diff --git a/cmd/discreteLog.go b/cmd/discreteLog.go
index a3259ef..f47c8e6 100644
--- a/cmd/discreteLog.go
+++ b/cmd/discreteLog.go
@@ -41,6 +41,11 @@ func ceilSqrt(x *big.Int) *big.Int {
 }
 
 func babyStepGiantStep(n, g, x, order *big.Int) (*big.Int, error) {
+	z := new(big.Int).GCD(nil, nil, g, n)
+	if z.Cmp(big.NewInt(1)) != 0 {
+		return nil, fmt.Errorf("base %v is not invertible modulo %v", g, n)
+	}
+
 	var m *big.Int
 	if order == nil {
 		// m = ceil(sqrt(n - 1))