diff --git a/config/variable_test.go b/config/variable_test.go
index c8b763405..a7f11e9f8 100644
--- a/config/variable_test.go
+++ b/config/variable_test.go
@@ -32,6 +32,22 @@ func TestVariableDetectWalker(t *testing.T) {
 	}
 }
 
+func TestVariableDetectWalker_resource(t *testing.T) {
+	w := new(variableDetectWalker)
+
+	str := `foo ${ec2.foo.bar}`
+	if err := w.Primitive(reflect.ValueOf(str)); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if len(w.Variables) != 1 {
+		t.Fatalf("bad: %#v", w.Variables)
+	}
+	if w.Variables["ec2.foo.bar"].(*ResourceVariable).FullKey() != "ec2.foo.bar" {
+		t.Fatalf("bad: %#v", w.Variables)
+	}
+}
+
 func TestVariableDetectWalker_bad(t *testing.T) {
 	w := new(variableDetectWalker)