diff --git a/plugin.go b/plugin.go
index e4dca05..cdfb30a 100644
--- a/plugin.go
+++ b/plugin.go
@@ -12,6 +12,11 @@ import (
 	"golang.org/x/crypto/ssh"
 )
 
+const (
+	missingHostOrUser    = "Error: missing server host or user"
+	missingPasswordOrKey = "Error: can't connect without a private SSH key or password"
+)
+
 type (
 	// Config for the plugin.
 	Config struct {
@@ -33,8 +38,12 @@ type (
 
 // Exec executes the plugin.
 func (p Plugin) Exec() error {
+	if len(p.Config.Host) == 0 && p.Config.User == "" {
+		return fmt.Errorf(missingHostOrUser)
+	}
+
 	if p.Config.Key == "" && p.Config.Password == "" {
-		return fmt.Errorf("Error: can't connect without a private SSH key or password")
+		return fmt.Errorf(missingPasswordOrKey)
 	}
 
 	for i, host := range p.Config.Host {
diff --git a/plugin_test.go b/plugin_test.go
index c041ffb..fc56ad5 100644
--- a/plugin_test.go
+++ b/plugin_test.go
@@ -6,6 +6,15 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestMissingHostOrUser(t *testing.T) {
+	plugin := Plugin{}
+
+	err := plugin.Exec()
+
+	assert.NotNil(t, err)
+	assert.Equal(t, missingHostOrUser, err.Error())
+}
+
 func TestMissingKeyOrPassword(t *testing.T) {
 	plugin := Plugin{
 		Config{
@@ -17,4 +26,5 @@ func TestMissingKeyOrPassword(t *testing.T) {
 	err := plugin.Exec()
 
 	assert.NotNil(t, err)
+	assert.Equal(t, missingPasswordOrKey, err.Error())
 }