diff --git a/.eslintrc.js b/.eslintrc.js
index 53e8cf888a18e..18763807cb36b 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -110,6 +110,7 @@ const restrictedImports = [
 			'maxBy',
 			'memoize',
 			'merge',
+			'mergeWith',
 			'negate',
 			'noop',
 			'nth',
diff --git a/package-lock.json b/package-lock.json
index dba43ade0dc9b..8a1b97e65c5de 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17859,8 +17859,10 @@
 				"@wordpress/wordcount": "file:packages/wordcount",
 				"classnames": "^2.3.1",
 				"colord": "^2.9.2",
+				"deepmerge": "^4.3.0",
 				"downloadjs": "^1.4.7",
 				"fast-deep-equal": "^3.1.3",
+				"is-plain-object": "^5.0.0",
 				"lodash": "^4.17.21",
 				"memize": "^2.1.0",
 				"react-autosize-textarea": "^7.1.0",
@@ -17871,6 +17873,11 @@
 					"version": "2.9.2",
 					"resolved": "https://registry.npmjs.org/colord/-/colord-2.9.2.tgz",
 					"integrity": "sha512-Uqbg+J445nc1TKn4FoDPS6ZZqAvEDnwrH42yo8B40JSOgSLxMZ/gt3h4nmCtPLQeXhjJJkqBx7SCY35WnIixaQ=="
+				},
+				"deepmerge": {
+					"version": "4.3.1",
+					"resolved": "https://registry.npmjs.org/deepmerge/-/deepmerge-4.3.1.tgz",
+					"integrity": "sha512-3sUqbMEc77XqpdNO7FRyRog+eW3ph+GYCbj+rK+uYyRMuwsVy0rMiVtPn+QJlKFvWP/1PYpapqYn0Me2knFn+A=="
 				}
 			}
 		},
diff --git a/packages/edit-site/package.json b/packages/edit-site/package.json
index 9108d71f83970..381f29a82e95f 100644
--- a/packages/edit-site/package.json
+++ b/packages/edit-site/package.json
@@ -66,8 +66,10 @@
 		"@wordpress/wordcount": "file:../wordcount",
 		"classnames": "^2.3.1",
 		"colord": "^2.9.2",
+		"deepmerge": "^4.3.0",
 		"downloadjs": "^1.4.7",
 		"fast-deep-equal": "^3.1.3",
+		"is-plain-object": "^5.0.0",
 		"lodash": "^4.17.21",
 		"memize": "^2.1.0",
 		"react-autosize-textarea": "^7.1.0",
diff --git a/packages/edit-site/src/components/global-styles/global-styles-provider.js b/packages/edit-site/src/components/global-styles/global-styles-provider.js
index 829563342e847..f666e48c6febe 100644
--- a/packages/edit-site/src/components/global-styles/global-styles-provider.js
+++ b/packages/edit-site/src/components/global-styles/global-styles-provider.js
@@ -1,7 +1,8 @@
 /**
  * External dependencies
  */
-import { mergeWith } from 'lodash';
+import deepmerge from 'deepmerge';
+import { isPlainObject } from 'is-plain-object';
 
 /**
  * WordPress dependencies
@@ -21,17 +22,13 @@ const { GlobalStylesContext, cleanEmptyObject } = unlock(
 	blockEditorPrivateApis
 );
 
-function mergeTreesCustomizer( _, srcValue ) {
-	// We only pass as arrays the presets,
-	// in which case we want the new array of values
-	// to override the old array (no merging).
-	if ( Array.isArray( srcValue ) ) {
-		return srcValue;
-	}
-}
-
 export function mergeBaseAndUserConfigs( base, user ) {
-	return mergeWith( {}, base, user, mergeTreesCustomizer );
+	return deepmerge( base, user, {
+		// We only pass as arrays the presets,
+		// in which case we want the new array of values
+		// to override the old array (no merging).
+		isMergeableObject: isPlainObject,
+	} );
 }
 
 function useGlobalStylesUserConfig() {