diff --git a/content.go b/content.go
index 31b1142..2585cd7 100644
--- a/content.go
+++ b/content.go
@@ -31,6 +31,10 @@ type (
 	}
 )
 
+// ErrInvalidDataType is returned when ContentFormat function are passed a data argument of invalid
+// type.
+var ErrInvalidDataType = errors.New("invalid data type")
+
 // ContentFormat transforms data to a DOM-based format to represent the content of the page.
 func ContentFormat(data interface{}) ([]Node, error) {
 	var doc html.Node
@@ -54,7 +58,7 @@ func ContentFormat(data interface{}) ([]Node, error) {
 		}
 		doc = *dom
 	default:
-		return nil, errors.New("invalid data type, use []byte or string")
+		return nil, ErrInvalidDataType
 	}
 
 	var content []Node
diff --git a/invalid_test.go b/invalid_test.go
index 07db307..25b4f07 100644
--- a/invalid_test.go
+++ b/invalid_test.go
@@ -11,7 +11,7 @@ const (
 var invalidAccount = &Account{}
 
 func TestInvalidContentFormat(t *testing.T) {
-	if _, err := ContentFormat(invalidContent); err == nil {
+	if _, err := ContentFormat(invalidContent); err != ErrInvalidDataType {
 		t.Error()
 	}
 }