diff --git a/kong_test.go b/kong_test.go
index f1e8e47..ad0d988 100644
--- a/kong_test.go
+++ b/kong_test.go
@@ -566,3 +566,14 @@ func TestErrorMissingArgs(t *testing.T) {
 	require.Error(t, err)
 	require.Equal(t, "expected \"<one> <two>\"", err.Error())
 }
+
+func TestBoolOverride(t *testing.T) {
+	var cli struct {
+		Flag bool `default:"true"`
+	}
+	p := mustNew(t, &cli)
+	_, err := p.Parse([]string{"--flag=false"})
+	require.NoError(t, err)
+	_, err = p.Parse([]string{"--flag", "false"})
+	require.Error(t, err)
+}
diff --git a/mapper.go b/mapper.go
index 20d1dac..3f980c2 100644
--- a/mapper.go
+++ b/mapper.go
@@ -211,7 +211,12 @@ func (r *Registry) RegisterDefaults() *Registry {
 type boolMapper struct{}
 
 func (boolMapper) Decode(ctx *DecodeContext, target reflect.Value) error {
-	target.SetBool(true)
+	if ctx.Scan.Peek().Type == FlagValueToken {
+		token := ctx.Scan.Pop()
+		target.SetBool(token.Value == "true")
+	} else {
+		target.SetBool(true)
+	}
 	return nil
 }
 func (boolMapper) IsBool() bool { return true }