diff --git a/schema/enum.go b/schema/enum.go
index 4783ccff6fc6..b52b01e1a522 100644
--- a/schema/enum.go
+++ b/schema/enum.go
@@ -41,7 +41,8 @@ func (e EnumType) TypeName() string {
 	return e.Name
 }
 
-func (EnumType) isType() {}
+func (EnumType) isType()          {}
+func (EnumType) isReferenceType() {}
 
 // Validate validates the enum definition.
 func (e EnumType) Validate(TypeSet) error {
diff --git a/schema/type.go b/schema/type.go
index 9728675cd836..a1205ad722a5 100644
--- a/schema/type.go
+++ b/schema/type.go
@@ -13,6 +13,15 @@ type Type interface {
 	isType()
 }
 
+// ReferenceType is a marker interface that all types that can be the target of Field.ReferencedType implement.
+// Currently, this is only EnumType.
+type ReferenceType interface {
+	Type
+
+	// IsReferenceType is implemented if this is a reference type.
+	isReferenceType()
+}
+
 // TypeSet represents something that has types and allows them to be looked up by name.
 // Currently, the only implementation is ModuleSchema.
 type TypeSet interface {