diff --git a/index.js b/index.js
index ef6a572..ad95f56 100644
--- a/index.js
+++ b/index.js
@@ -4,6 +4,7 @@ const assureArray = require("assure-array");
 const isPlainObj = require("is-plain-obj");
 const defaultValue = require("default-value");
 const flat = require("array.prototype.flat");
+const flatMap = require("array.prototype.flatmap");
 
 const matchSpecial = require("@validatem/match-special");
 const isPlainObjectValidator = require("@validatem/is-plain-object");
@@ -19,7 +20,7 @@ module.exports = function normalizeRules(rules, options) {
 	let actualRules = flattened.filter((rule) => rule != null);
 
 	if (normalizeObjects) {
-		return actualRules.flatMap((rule) => {
+		return flatMap(actualRules, (rule) => {
 			if (isPlainObj(rule) && !matchSpecial(rule)) {
 				return [
 					isPlainObjectValidator,
diff --git a/package.json b/package.json
index f9b0a25..daf3059 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
     "@validatem/is-plain-object": "^0.1.0",
     "@validatem/match-special": "^0.1.0",
     "array.prototype.flat": "^1.2.3",
+    "array.prototype.flatmap": "^1.2.3",
     "assure-array": "^1.0.0",
     "default-value": "^1.0.0",
     "is-plain-obj": "^2.1.0"
diff --git a/yarn.lock b/yarn.lock
index 4cebdec..0840259 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -164,6 +164,15 @@ array.prototype.flat@^1.2.3:
     define-properties "^1.1.3"
     es-abstract "^1.17.0-next.1"
 
+array.prototype.flatmap@^1.2.3:
+  version "1.2.3"
+  resolved "https://registry.yarnpkg.com/array.prototype.flatmap/-/array.prototype.flatmap-1.2.3.tgz#1c13f84a178566042dd63de4414440db9222e443"
+  integrity sha512-OOEk+lkePcg+ODXIpvuU9PAryCikCJyo7GlDG1upleEpQRx6mzL9puEBkozQ5iAx20KV0l3DbyQwqciJtqe5Pg==
+  dependencies:
+    define-properties "^1.1.3"
+    es-abstract "^1.17.0-next.1"
+    function-bind "^1.1.1"
+
 as-expression@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/as-expression/-/as-expression-1.0.0.tgz#7bc620ca4cb2fe0ee90d86729bd6add33b8fd831"