diff --git a/index.js b/index.js
index d1a695e..dda3741 100644
--- a/index.js
+++ b/index.js
@@ -2,7 +2,6 @@
 
 var hasSymbols = require('has-symbols')();
 var isSymbol = require('is-symbol');
-var flatMap = require('array.prototype.flatmap');
 var ownKeys = require('reflect.ownkeys');
 var callBound = require('call-bound');
 
@@ -11,19 +10,17 @@ var result;
 
 if (hasSymbols) {
 	var symbolValueOf = callBound('Symbol.prototype.valueOf');
-	var wellKnownSymbols = hasSymbols && flatMap(
-		ownKeys(Symbol),
-		function (k) {
-			var v = Symbol[k];
-			// eslint-disable-next-line no-extra-parens
-			return typeof v === 'symbol' ? /** @type {[import('.').WellKnownSymbol]} */ (/** @type {unknown} */ (v)) : [];
-		}
-	);
+	var symKeys = ownKeys(Symbol);
 
 	/** @type {{ __proto__: null } & { [k in import('.').WellKnownSymbol]?: true }} */
 	var map = { __proto__: null };
-	for (var i = 0; i < wellKnownSymbols.length; i += 1) {
-		map[wellKnownSymbols[i]] = true;
+
+	for (var i = 0; i < symKeys.length; i += 1) {
+		var v = Symbol[symKeys[i]];
+		if (typeof v === 'symbol') {
+			// eslint-disable-next-line no-extra-parens
+			map[/** @type {import('.').WellKnownSymbol} */ (/** @type {unknown} */ (v))] = true;
+		}
 	}
 
 	result = /** @type {import('.')} */ function isWellKnownSymbol(sym) {
diff --git a/package.json b/package.json
index eaaead6..96e38da 100644
--- a/package.json
+++ b/package.json
@@ -42,7 +42,6 @@
 	},
 	"homepage": "https://github.com/inspect-js/is-well-known-symbol#readme",
 	"dependencies": {
-		"array.prototype.flatmap": "^1.3.3",
 		"call-bound": "^1.0.3",
 		"has-symbols": "^1.1.0",
 		"is-symbol": "^1.1.1",
@@ -52,7 +51,6 @@
 		"@arethetypeswrong/cli": "^0.17.1",
 		"@ljharb/eslint-config": "^21.1.1",
 		"@ljharb/tsconfig": "^0.2.2",
-		"@types/array.prototype.flatmap": "^1.2.6",
 		"@types/for-each": "^0.3.3",
 		"@types/object-inspect": "^1.13.0",
 		"@types/reflect.ownkeys": "^1.1.0",