diff --git a/src/Assets/Assets.php b/src/Assets/Assets.php
index c3302ea..f389b04 100755
--- a/src/Assets/Assets.php
+++ b/src/Assets/Assets.php
@@ -2,6 +2,8 @@
 
 namespace StellarWP\Assets;
 
+use InvalidArgumentException;
+
 class Assets {
 	/**
 	 * @var ?Assets
@@ -676,8 +678,9 @@ protected function do_enqueue( Asset $asset, bool $force_enqueue = false ): void
 	 * Register the Assets on the correct hooks.
 	 *
 	 * @since 1.0.0
+	 * @since 1.4.5 Ensure the method accepts only `null` or an `Asset` instance or an array of `Asset[]` instances.
 	 *
-	 * @param array|Asset|null $assets Array of asset objects, single asset object, or null.
+	 * @param Asset[]|Asset|null $assets Array of asset objects, single asset object, or null.
 	 *
 	 * @return void
 	 */
@@ -688,25 +691,27 @@ public function register_in_wp( $assets = null ) {
 		)
 		) {
 			// Registering the asset now would trigger a doing_it_wrong notice: queue the assets to be registered later.
-			if ( $assets === null ) {
+			if ( $assets === null || empty( $assets ) ) {
 				return;
 			}
 
 			if ( ! is_array( $assets ) ) {
-				if ( ! $assets instanceof Asset ) {
-					throw new \InvalidArgumentException( 'Assets in register_in_wp() must be of type Asset' );
+				$assets = [ $assets ];
+			}
+
+			foreach ( $assets as $asset ) {
+				if ( ! $asset instanceof Asset ) {
+					throw new InvalidArgumentException( 'Assets in register_in_wp() must be of type Asset' );
 				}
 
-				$assets = [ $assets->get_slug() => $assets ];
+				// Register later, avoid the doing_it_wrong notice.
+				$this->assets[ $asset->get_slug() ] = $asset;
 			}
 
-			// Register later, avoid the doing_it_wrong notice.
-			$this->assets = array_merge( $this->assets, $assets );
-
 			return;
 		}
 
-		if ( is_null( $assets ) ) {
+		if ( null === $assets ) {
 			$assets = $this->get();
 		}
 
@@ -714,7 +719,15 @@ public function register_in_wp( $assets = null ) {
 			$assets = [ $assets ];
 		}
 
+		if ( empty( $assets ) ) {
+			return;
+		}
+
 		foreach ( $assets as $asset ) {
+			if ( ! $asset instanceof Asset ) {
+				throw new InvalidArgumentException( 'Assets in register_in_wp() must be of type Asset' );
+			}
+
 			// Asset is already registered.
 			if ( $asset->is_registered() ) {
 				continue;
diff --git a/tests/wpunit/AssetsTest.php b/tests/wpunit/AssetsTest.php
index 86af111..5775d11 100644
--- a/tests/wpunit/AssetsTest.php
+++ b/tests/wpunit/AssetsTest.php
@@ -4,6 +4,10 @@
 
 use StellarWP\Assets\Tests\AssetTestCase;
 use PHPUnit\Framework\Assert;
+use stdClass;
+use Closure;
+use Generator;
+use InvalidArgumentException;
 
 class AssetsTest extends AssetTestCase {
 	/**
@@ -43,6 +47,56 @@ public function unset_uopz_redefines() {
 		self::$uopz_redefines = [];
 	}
 
+	public function it_should_accept_instance_of_asset_or_array_of_assets_in_register_in_wp() {
+		$asset_1 = Asset::add( 'fake1-script', 'fake1.js' );
+		$asset_2 = Asset::add( 'fake1-style', 'fake1.css' );
+		$asset_3 = Asset::add( 'fake2-script', 'fake2.js' );
+		$asset_4 = Asset::add( 'fake2-style', 'fake2.css' );
+		$asset_5 = Asset::add( 'fake3-script', 'fake3.js' );
+
+		$assets = Assets::init();
+
+		$assets->register_in_wp( null ); // No problemo... nothing happens though.
+		$assets->register_in_wp( [] ); // No problemo... nothing happens though.
+
+		$this->assertFalse( $asset_1->is_registered() );
+		$assets->register_in_wp( $asset_1 );
+		$this->assertTrue( $asset_1->is_registered() );
+
+		$this->assertFalse( $asset_2->is_registered() );
+		$this->assertFalse( $asset_3->is_registered() );
+		$this->assertFalse( $asset_4->is_registered() );
+		$this->assertFalse( $asset_5->is_registered() );
+		$assets->register_in_wp( [ $asset_2, $asset_3, $asset_4, $asset_5 ] );
+		$this->assertTrue( $asset_2->is_registered() );
+		$this->assertTrue( $asset_3->is_registered() );
+		$this->assertTrue( $asset_4->is_registered() );
+		$this->assertTrue( $asset_5->is_registered() );
+	}
+
+	public function invalid_params_for_register_in_wp_provider(): Generator {
+		yield 'string'         => [ fn() => 'string' ];
+		yield 'int'            => [ fn() => 1 ];
+		yield 'float'          => [ fn() => 1.1 ];
+		yield 'bool - true'    => [ fn() => true ];
+		yield 'bool - false'   => [ fn() => false ];
+		yield 'object'         => [ fn() => new stdClass() ];
+		yield 'array - mixed'  => [ fn () => [ Asset::add( 'fake1-script', 'fake1.js' ), 'string' ] ];
+	}
+
+	/**
+	 * @test
+	 * @dataProvider invalid_params_for_register_in_wp_provider
+	 */
+	public function it_should_throw_exception_when_invalid_params_are_passed_to_register_in_wp( Closure $fixture ) {
+		$assets = Assets::init();
+
+		$this->expectException( InvalidArgumentException::class );
+		$this->expectExceptionMessage( 'Assets in register_in_wp() must be of type Asset' );
+
+		$assets->register_in_wp( $fixture() );
+	}
+
 	/**
 	 * @test
 	 */