diff --git a/module/validator_set.go b/module/validator_set.go
index ebddaea..fff240b 100644
--- a/module/validator_set.go
+++ b/module/validator_set.go
@@ -23,10 +23,14 @@ func (v Validators) Contains(other Validators) bool {
 			}
 		}
 	}
-	required := ceilDiv(len(v), 3)
+	required := v.threshold()
 	return count >= required
 }
 
+func (v Validators) threshold() int {
+	return len(v) - ceilDiv(len(v)*2, 3) + 1
+}
+
 func ceilDiv(x, y int) int {
 	if y == 0 {
 		return 0
diff --git a/module/validator_set_test.go b/module/validator_set_test.go
index 0d09b12..555300c 100644
--- a/module/validator_set_test.go
+++ b/module/validator_set_test.go
@@ -90,7 +90,7 @@ func (ts *ValidatorSetTestSuite) TestCheckpoint() {
 	ts.Equal(int(validator.Checkpoint(9)), 99)
 }
 
-func (ts *ValidatorSetTestSuite) TestValidator() {
+func (ts *ValidatorSetTestSuite) TestTrustValidator() {
 	trusted := Validators([][]byte{{1}, {2}, {3}, {4}, {5}})
 	ts.True(trusted.Contains([][]byte{{1}, {2}, {3}, {4}, {5}}))
 	ts.True(trusted.Contains([][]byte{{1}, {2}, {3}, {4}, {5}, {10}, {11}, {12}, {13}, {14}}))
@@ -104,5 +104,17 @@ func (ts *ValidatorSetTestSuite) TestValidator() {
 	ts.False(trusted.Contains([][]byte{{1}, {10}, {11}, {12}, {13}, {14}}))
 	ts.False(trusted.Contains([][]byte{}))
 	ts.False(trusted.Contains([][]byte{{10}, {11}, {12}, {13}, {14}}))
+}
 
+func (ts *ValidatorSetTestSuite) TestThreshold() {
+	ts.Equal(1, Validators(make([][]byte, 1)).threshold())
+	ts.Equal(1, Validators(make([][]byte, 2)).threshold())
+	ts.Equal(2, Validators(make([][]byte, 3)).threshold())
+	ts.Equal(2, Validators(make([][]byte, 4)).threshold())
+	ts.Equal(2, Validators(make([][]byte, 5)).threshold())
+	ts.Equal(3, Validators(make([][]byte, 6)).threshold())
+	ts.Equal(3, Validators(make([][]byte, 7)).threshold())
+	ts.Equal(3, Validators(make([][]byte, 8)).threshold())
+	ts.Equal(4, Validators(make([][]byte, 9)).threshold())
+	ts.Equal(8, Validators(make([][]byte, 21)).threshold())
 }