diff --git a/invalidutf8.go b/invalidutf8.go
new file mode 100644
index 0000000..e6100f6
--- /dev/null
+++ b/invalidutf8.go
@@ -0,0 +1,16 @@
+package utf8s
+
+type InvalidUTF8Complainer interface {
+	error
+	InvalidUTF8Complainer()
+}
+
+type internalInvalidUTF8Complainer struct{}
+
+func (complainer internalInvalidUTF8Complainer) Error() string {
+	return "Invalid UTF-8"
+}
+
+func (complainer internalInvalidUTF8Complainer) InvalidUTF8Complainer() {
+	// Nothing here.
+}