diff --git a/package-lock.json b/package-lock.json
index dd23690..0e653d9 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,6 +9,7 @@
       "version": "2.1.2",
       "license": "Apache-2.0",
       "dependencies": {
+        "@jridgewell/set-array": "1.0.0",
         "@jridgewell/trace-mapping": "^0.3.0"
       },
       "devDependencies": {
@@ -1026,6 +1027,14 @@
         "node": ">=6.0.0"
       }
     },
+    "node_modules/@jridgewell/set-array": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/@jridgewell/set-array/-/set-array-1.0.0.tgz",
+      "integrity": "sha512-LcqVnHCjOAj8BTCtjpwYZCMTn4yArusbdObCVRUYvBHhrR5fVLVyENG+UVWM4T4H/ufv7NiBLdprllxWs/5PaQ==",
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
     "node_modules/@jridgewell/sourcemap-codec": {
       "version": "1.4.10",
       "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.4.10.tgz",
@@ -6790,6 +6799,11 @@
       "resolved": "https://registry.npmjs.org/@jridgewell/resolve-uri/-/resolve-uri-3.0.4.tgz",
       "integrity": "sha512-cz8HFjOFfUBtvN+NXYSFMHYRdxZMaEl0XypVrhzxBgadKIXhIkRd8aMeHhmF56Sl7SuS8OnUpQ73/k9LE4VnLg=="
     },
+    "@jridgewell/set-array": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/@jridgewell/set-array/-/set-array-1.0.0.tgz",
+      "integrity": "sha512-LcqVnHCjOAj8BTCtjpwYZCMTn4yArusbdObCVRUYvBHhrR5fVLVyENG+UVWM4T4H/ufv7NiBLdprllxWs/5PaQ=="
+    },
     "@jridgewell/sourcemap-codec": {
       "version": "1.4.10",
       "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.4.10.tgz",
diff --git a/package.json b/package.json
index 0914a04..e51667b 100644
--- a/package.json
+++ b/package.json
@@ -57,6 +57,7 @@
     "typescript": "4.5.5"
   },
   "dependencies": {
+    "@jridgewell/set-array": "^1.0.0",
     "@jridgewell/trace-mapping": "^0.3.0"
   }
 }
diff --git a/src/fast-string-array.ts b/src/fast-string-array.ts
deleted file mode 100644
index 04bf285..0000000
--- a/src/fast-string-array.ts
+++ /dev/null
@@ -1,38 +0,0 @@
-export interface FastStringArray {
-  indexes: { [key: string]: number };
-  array: readonly string[];
-}
-
-/**
- * FastStringArray acts like a `Set` (allowing only one occurrence of a string
- * `key`), but provides the index of the `key` in the backing array.
- *
- * This is designed to allow synchronizing a second array with the contents of
- * the backing array, like how `sourcesContent[i]` is the source content
- * associated with `source[i]`, and there are never duplicates.
- */
-export function FastStringArray(): FastStringArray {
-  return {
-    indexes: { __proto__: null } as any,
-    array: [],
-  };
-}
-
-/**
- * Puts `key` into the backing array, if it is not already present. Returns
- * the index of the `key` in the backing array.
- */
-export function put(strarr: FastStringArray, key: string): number {
-  const { array, indexes } = strarr;
-  // The key may or may not be present. If it is present, it's a number.
-  let index = indexes[key] as number | undefined;
-
-  // If it's not yet present, we need to insert it and track the index in the
-  // indexes.
-  if (index === undefined) {
-    index = indexes[key] = array.length;
-    (array as string[]).push(key);
-  }
-
-  return index;
-}
diff --git a/src/source-map-tree.ts b/src/source-map-tree.ts
index c815ade..d029976 100644
--- a/src/source-map-tree.ts
+++ b/src/source-map-tree.ts
@@ -1,4 +1,4 @@
-import { FastStringArray, put } from './fast-string-array';
+import { SetArray, put } from '@jridgewell/set-array';
 import { presortedDecodedMap, traceSegment, decodedMappings } from '@jridgewell/trace-mapping';
 
 import type { TraceMap } from '@jridgewell/trace-mapping';
@@ -62,8 +62,8 @@ export function OriginalSource(source: string, content: string | null): Original
  */
 export function traceMappings(tree: Sources): TraceMap {
   const mappings: SourceMapSegment[][] = [];
-  const names = FastStringArray();
-  const sources = FastStringArray();
+  const names = new SetArray();
+  const sources = new SetArray();
   const sourcesContent: (string | null)[] = [];
   const { sources: rootSources, map } = tree;
   const rootNames = map.names;
diff --git a/test/unit/fast-array-string.ts b/test/unit/fast-array-string.ts
deleted file mode 100644
index a7fce35..0000000
--- a/test/unit/fast-array-string.ts
+++ /dev/null
@@ -1,52 +0,0 @@
-import { FastStringArray, put } from '../../src/fast-string-array';
-
-describe('FastStringArray', () => {
-  describe('put()', () => {
-    test('puts string in if not present', () => {
-      const array = FastStringArray();
-
-      put(array, 'test');
-      expect(array.array).toEqual(['test']);
-      put(array, 'test');
-      expect(array.array).toEqual(['test']);
-
-      put(array, 'foo');
-      expect(array.array).toEqual(['test', 'foo']);
-      put(array, 'bar');
-      expect(array.array).toEqual(['test', 'foo', 'bar']);
-
-      put(array, 'bar');
-      expect(array.array).toEqual(['test', 'foo', 'bar']);
-      put(array, 'foo');
-      expect(array.array).toEqual(['test', 'foo', 'bar']);
-    });
-
-    test('returns index of string in array', () => {
-      const array = FastStringArray();
-
-      expect(put(array, 'test')).toBe(0);
-      expect(put(array, 'foo')).toBe(1);
-      expect(put(array, 'bar')).toBe(2);
-    });
-
-    test('returns original index of string in array', () => {
-      const array = FastStringArray();
-
-      put(array, 'test');
-      put(array, 'foo');
-      put(array, 'bar');
-
-      expect(put(array, 'test')).toBe(0);
-      expect(put(array, 'foo')).toBe(1);
-      expect(put(array, 'bar')).toBe(2);
-    });
-
-    test('handles empty string', () => {
-      const array = FastStringArray();
-
-      expect(put(array, '')).toBe(0);
-      expect(put(array, '')).toBe(0);
-      expect(array.array).toEqual(['']);
-    });
-  });
-});