diff --git a/graphile-build/graphile-build/src/vendor/collectReferencedTypes.ts b/graphile-build/graphile-build/src/vendor/collectReferencedTypes.ts
new file mode 100644
index 000000000..346006a2f
--- /dev/null
+++ b/graphile-build/graphile-build/src/vendor/collectReferencedTypes.ts
@@ -0,0 +1,70 @@
+import type { GraphQLNamedType, GraphQLType } from "graphql";
+import {
+  getNamedType,
+  isInputObjectType,
+  isInterfaceType,
+  isObjectType,
+  isUnionType,
+} from "graphql";
+
+/*
+Copy of https://github.com/graphql/graphql-js/blob/45e28a5b74cfa811857e7a4694b095da284d14eb/src/type/schema.ts#L406-L437
+
+Used as permitted by the license:
+
+MIT License
+
+Copyright (c) GraphQL Contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+*/
+
+export function collectReferencedTypes(
+  type: GraphQLType,
+  typeSet: Set<GraphQLNamedType>,
+): Set<GraphQLNamedType> {
+  const namedType = getNamedType(type);
+
+  if (!typeSet.has(namedType)) {
+    typeSet.add(namedType);
+    if (isUnionType(namedType)) {
+      for (const memberType of namedType.getTypes()) {
+        collectReferencedTypes(memberType, typeSet);
+      }
+    } else if (isObjectType(namedType) || isInterfaceType(namedType)) {
+      for (const interfaceType of namedType.getInterfaces()) {
+        collectReferencedTypes(interfaceType, typeSet);
+      }
+
+      for (const field of Object.values(namedType.getFields())) {
+        collectReferencedTypes(field.type, typeSet);
+        for (const arg of field.args) {
+          collectReferencedTypes(arg.type, typeSet);
+        }
+      }
+    } else if (isInputObjectType(namedType)) {
+      for (const field of Object.values(namedType.getFields())) {
+        collectReferencedTypes(field.type, typeSet);
+      }
+    }
+  }
+
+  return typeSet;
+}