diff --git a/tools/src/helpers.ts b/tools/src/helpers.ts
index f584629dd..be9aa209f 100644
--- a/tools/src/helpers.ts
+++ b/tools/src/helpers.ts
@@ -77,18 +77,11 @@ export function delete_matching_keys(obj: any, condition: (obj: any) => boolean)
   }
 }
 
-export function find_refs(obj: Record<string, any>): string[] {
-  let results: string[] = []
-
-  if (obj !== undefined && obj !== null && obj.$ref !== undefined) {
-    results.push(obj.$ref as string)
-  }
-
-  if (_.isObject(obj)) {
-    results = _.concat(results, _.flatMap(obj, (v, _k) => find_refs(v as Record<string, any>)))
-  }
-
-  return _.uniq(results)
+export function find_refs (obj: any): Set<string> {
+  var results = new Set<string>()
+  if (obj?.$ref != null) results.add(obj.$ref as string)
+  if (_.isObject(obj)) _.forEach(obj, (v) => find_refs(v).forEach((ref) => results.add(ref)))
+  return results
 }
 
 export function ensure_parent_dir (file_path: string): void {
diff --git a/tools/src/merger/OpenApiVersionExtractor.ts b/tools/src/merger/OpenApiVersionExtractor.ts
index 2c0ce0f57..5d4164b1c 100644
--- a/tools/src/merger/OpenApiVersionExtractor.ts
+++ b/tools/src/merger/OpenApiVersionExtractor.ts
@@ -52,9 +52,9 @@ export default class OpenApiVersionExtractor {
     const x_version_added = semver.coerce(obj['x-version-added'] as string)
     const x_version_removed = semver.coerce(obj['x-version-removed'] as string)
 
-    if (x_version_added && !semver.satisfies(this._target_version, `>=${x_version_added?.toString()}`)) {
+    if (x_version_added && !semver.satisfies(this._target_version, `>=${x_version_added.toString()}`)) {
       return true
-    } else if (x_version_removed && !semver.satisfies(this._target_version, `<${x_version_removed?.toString()}`)) {
+    } else if (x_version_removed && !semver.satisfies(this._target_version, `<${x_version_removed.toString()}`)) {
       return true
     }
 
@@ -70,13 +70,15 @@ export default class OpenApiVersionExtractor {
     if (this._spec === undefined) return
 
     // remove anything that's not referenced
-    var references: string[] = find_refs(this._spec)
+    var references = find_refs(this._spec)
 
     this._spec.components = _.reduce(_.map(['parameters', 'requestBodies', 'responses', 'schemas'], (p) =>
     {
       return {
-        [p]: _.pickBy(this._spec?.components?.[p], (_value, key) =>
-          _.includes(references, `#/components/${p}/${key}`))
+        [p]: _.pickBy(
+          this._spec?.components?.[p], (_value, key) =>
+            references.has(`#/components/${p}/${key}`)
+        )
       }
     }
     ), extend)
diff --git a/tools/tests/helpers.test.ts b/tools/tests/helpers.test.ts
index 1991d21b6..185ca6415 100644
--- a/tools/tests/helpers.test.ts
+++ b/tools/tests/helpers.test.ts
@@ -126,7 +126,7 @@ describe('helpers', () => {
 
   describe('find_refs', () => {
     test('empty collection', () => {
-      expect(find_refs({})).toEqual([])
+      expect(find_refs({})).toEqual(new Set())
     })
 
     test('with refs', () => {
@@ -148,7 +148,7 @@ describe('helpers', () => {
             $ref: 'dup',
           },
         }]
-      })).toEqual([1, 2, 3, 'dup'])
+      })).toEqual(new Set([1, 2, 3, 'dup']))
     })
   })
 })