diff --git a/phpunit/tests/fonts/font-library/wpRestFontLibraryController/installFonts.php b/phpunit/tests/fonts/font-library/wpRestFontLibraryController/installFonts.php
index 8b8ec28406ac1d..5edcf054e2d025 100644
--- a/phpunit/tests/fonts/font-library/wpRestFontLibraryController/installFonts.php
+++ b/phpunit/tests/fonts/font-library/wpRestFontLibraryController/installFonts.php
@@ -415,5 +415,60 @@ public function data_install_with_improper_inputs() {
 			),
 		);
 	}
+
+	/**
+	 * Tests that duplicate font faces with same font style and weight but different file extensions are merged.
+	 * 
+	 * @dataProvider data_install_with_duplicate_font_faces
+	 * @param array $font_families Font families to install in theme.json format.
+	 * @param array $files         Font files to install.
+	 */
+	public function test_install_with_duplicate_font_faces( $font_families, $files = array() ) {
+		$install_request    = new WP_REST_Request( 'POST', '/wp/v2/fonts' );
+		$font_families_json = json_encode( $font_families );
+		$install_request->set_param( 'fontFamilies', $font_families_json );
+		$install_request->set_file_params( $files );
+
+		$response = rest_get_server()->dispatch( $install_request );
+		$this->assertSame( 200, $response->get_status() );
+		$data = $response->get_data();
+
+		$this->assertCount( 1, $data[0]['fontFace'], 'Duplicate font faces were not removed / added incorrectly.' );
+		$this->assertSame( 'http://example.com/fonts/piazzolla_400_italic.ttf', $data[0]['fontFace'][0]['src'], 'The src attribute does not match the expected font file' );
+	}
+
+	/**
+	 * Data provider for test_install_with_duplicate_font_faces
+	 */
+	public function data_install_with_duplicate_font_faces() {
+		return array(
+			'with duplicate font faces' => array(
+				'font_families' => array(
+					array(
+						'fontFamily' => 'Piazzolla',
+						'slug'       => 'piazzolla',
+						'name'       => 'Piazzolla',
+						'fontFace'   => array(
+							array(
+								'fontFamily'      => 'Piazzolla',
+								'fontStyle'       => 'italic',
+								'fontWeight'      => '400',
+								'src'             => 'http://example.com/fonts/piazzolla_400_italic.ttf',
+								'downloadFromUrl' => 'http://example.com/fonts/piazzolla_400_italic.ttf',
+							),
+							array(
+								'fontFamily'      => 'Piazzolla',
+								'fontStyle'       => 'italic',
+								'fontWeight'      => '400',
+								'src'             => 'http://example.com/fonts/piazzolla_400_italic.woff',
+								'downloadFromUrl' => 'http://example.com/fonts/piazzolla_400_italic.woff',
+							),
+						),
+					),
+				),
+				'files'         => array(),
+			),
+		);
+	}
 }