diff --git a/index.js b/index.js
index ad95f56..59fe777 100644
--- a/index.js
+++ b/index.js
@@ -3,8 +3,7 @@
 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 flatten = require("flatten");
 
 const matchSpecial = require("@validatem/match-special");
 const isPlainObjectValidator = require("@validatem/is-plain-object");
@@ -15,12 +14,13 @@ const hasShape = require("@validatem/has-shape");
 module.exports = function normalizeRules(rules, options) {
 	let normalizeObjects = defaultValue(options.normalizeObjects, false);
 
-	// TODO: Switch to `Array#flat` once it is available
-	let flattened = flat(assureArray(rules));
+	// TODO: Switch to `Array#flat` once Node 10.x goes EOL (April 2021)
+	let flattened = flatten(assureArray(rules));
 	let actualRules = flattened.filter((rule) => rule != null);
 
 	if (normalizeObjects) {
-		return flatMap(actualRules, (rule) => {
+		// TODO: Switch to `Array#flatmap` once Node 10.x goes EOL (April 2021)
+		let mapped = actualRules.map((rule) => {
 			if (isPlainObj(rule) && !matchSpecial(rule)) {
 				return [
 					isPlainObjectValidator,
@@ -30,6 +30,8 @@ module.exports = function normalizeRules(rules, options) {
 				return rule;
 			}
 		});
+
+		return flatten(mapped);
 	} else {
 		return actualRules;
 	}
diff --git a/package.json b/package.json
index 32bec39..e8e2c52 100644
--- a/package.json
+++ b/package.json
@@ -10,10 +10,9 @@
     "@validatem/has-shape": "^0.1.0",
     "@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",
+    "flatten": "^1.0.3",
     "is-plain-obj": "^2.1.0"
   },
   "devDependencies": {
diff --git a/yarn.lock b/yarn.lock
index 0840259..fde5c11 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -164,15 +164,6 @@ 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"
@@ -522,6 +513,11 @@ flatted@^2.0.0:
   resolved "https://registry.yarnpkg.com/flatted/-/flatted-2.0.2.tgz#4575b21e2bcee7434aa9be662f4b7b5f9c2b5138"
   integrity sha512-r5wGx7YeOwNWNlCA0wQ86zKyDLMQr+/RB8xy74M4hTphfmjlijTSSXGuH8rnvKZnfT9i+75zmd8jcKdMR4O6jA==
 
+flatten@^1.0.3:
+  version "1.0.3"
+  resolved "https://registry.yarnpkg.com/flatten/-/flatten-1.0.3.tgz#c1283ac9f27b368abc1e36d1ff7b04501a30356b"
+  integrity sha512-dVsPA/UwQ8+2uoFe5GHtiBMu48dWLTdsuEd7CKGlZlD78r1TTWBvDuFaFGKCo/ZfEr95Uk56vZoX86OsHkUeIg==
+
 fs.realpath@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/fs.realpath/-/fs.realpath-1.0.0.tgz#1504ad2523158caa40db4a2787cb01411994ea4f"