diff --git a/src/wp-includes/fonts.php b/src/wp-includes/fonts.php
index 690aaa5ffc343..7c89186d0e40c 100644
--- a/src/wp-includes/fonts.php
+++ b/src/wp-includes/fonts.php
@@ -113,7 +113,7 @@ function wp_get_font_dir() {
 		$site_path = '/sites/' . get_current_blog_id();
 	}
 
-	$defaults = array(
+	$default_dir = array(
 		'path'    => path_join( WP_CONTENT_DIR, 'fonts' ) . $site_path,
 		'url'     => untrailingslashit( content_url( 'fonts' ) ) . $site_path,
 		'subdir'  => '',
@@ -131,7 +131,44 @@ function wp_get_font_dir() {
 	 *
 	 * @param array $defaults The original fonts directory data.
 	 */
-	return apply_filters( 'font_dir', $defaults );
+	$font_dir = apply_filters( 'font_dir', $default_dir );
+
+	wp_mkdir_p( $font_dir['path'] );
+
+	if ( ! is_dir( $font_dir['path'] ) || ! wp_is_writable( $font_dir['path'] ) ) {
+
+		// If the default directory was filtered it uses the filtered values and doesnt fall back to the wp-content/uploads/fonts.
+		if ( $font_dir !== $default_dir ) {
+			$font_dir['error'] = sprintf(
+				/* translators: %s: Directory path. */
+				__( 'Unable to create directory %s. Is its parent directory writable by the server?' ),
+				esc_html( str_replace( ABSPATH, '', $font_dir['path'] ) )
+			);
+			return $font_dir;
+		}
+
+		$upload_dir = wp_get_upload_dir();
+		$font_dir   = array(
+			'path'    => path_join( $upload_dir['basedir'], 'fonts' ),
+			'url'     => $upload_dir['baseurl'] . '/fonts',
+			'subdir'  => '',
+			'basedir' => path_join( $upload_dir['basedir'], 'fonts' ),
+			'baseurl' => $upload_dir['baseurl'] . '/fonts',
+			'error'   => false,
+		);
+
+		wp_mkdir_p( $font_dir['path'] );
+
+		if ( ! is_dir( $font_dir['path'] ) || ! wp_is_writable( $font_dir['path'] ) ) {
+			$font_dir['error'] = sprintf(
+				/* translators: %s: Directory path. */
+				__( 'Unable to create directory %s. Is its parent directory writable by the server?' ),
+				esc_html( str_replace( ABSPATH, '', $font_dir['path'] ) )
+			);
+		}
+	}
+
+	return $font_dir;
 }
 
 /**
diff --git a/tests/phpunit/tests/fonts/font-library/wpFontsDir.php b/tests/phpunit/tests/fonts/font-library/wpFontsDir.php
index a8f79888315bd..7c371f823ec28 100644
--- a/tests/phpunit/tests/fonts/font-library/wpFontsDir.php
+++ b/tests/phpunit/tests/fonts/font-library/wpFontsDir.php
@@ -16,30 +16,37 @@ class Tests_Fonts_WpFontDir extends WP_UnitTestCase {
 	public static function set_up_before_class() {
 		parent::set_up_before_class();
 
-		static::$dir_defaults = array(
-			'path'    => path_join( WP_CONTENT_DIR, 'fonts' ),
-			'url'     => content_url( 'fonts' ),
+		$path               = path_join( WP_CONTENT_DIR, 'fonts' );
+		$url                = content_url( 'fonts' );
+		self::$dir_defaults = array(
+			'path'    => $path,
+			'url'     => $url,
 			'subdir'  => '',
-			'basedir' => path_join( WP_CONTENT_DIR, 'fonts' ),
-			'baseurl' => content_url( 'fonts' ),
+			'basedir' => $path,
+			'baseurl' => $url,
 			'error'   => false,
 		);
 	}
 
+	public function tear_down() {
+		$this->remove_font_paths();
+		parent::tear_down();
+	}
+
 	public function test_fonts_dir() {
 		$font_dir = wp_get_font_dir();
 
 		$this->assertSame( $font_dir, static::$dir_defaults );
 	}
 
-	public function test_fonts_dir_with_filter() {
+	public function test_font_dir_filter() {
 		// Define a callback function to pass to the filter.
 		function set_new_values( $defaults ) {
-			$defaults['path']    = '/custom-path/fonts/my-custom-subdir';
-			$defaults['url']     = 'http://example.com/custom-path/fonts/my-custom-subdir';
-			$defaults['subdir']  = 'my-custom-subdir';
-			$defaults['basedir'] = '/custom-path/fonts';
-			$defaults['baseurl'] = 'http://example.com/custom-path/fonts';
+			$defaults['path']    = path_join( WP_CONTENT_DIR, 'custom_dir' );
+			$defaults['url']     = 'http://example.com/custom-path/fonts/my-custom-dir';
+			$defaults['subdir']  = '';
+			$defaults['basedir'] = path_join( WP_CONTENT_DIR, 'custom_dir' );
+			$defaults['baseurl'] = 'http://example.com/custom-path/fonts/my-custom-dir';
 			$defaults['error']   = false;
 			return $defaults;
 		}
@@ -51,11 +58,11 @@ function set_new_values( $defaults ) {
 		$font_dir = wp_get_font_dir();
 
 		$expected = array(
-			'path'    => '/custom-path/fonts/my-custom-subdir',
-			'url'     => 'http://example.com/custom-path/fonts/my-custom-subdir',
-			'subdir'  => 'my-custom-subdir',
-			'basedir' => '/custom-path/fonts',
-			'baseurl' => 'http://example.com/custom-path/fonts',
+			'path'    => path_join( WP_CONTENT_DIR, 'custom_dir' ),
+			'url'     => 'http://example.com/custom-path/fonts/my-custom-dir',
+			'subdir'  => '',
+			'basedir' => path_join( WP_CONTENT_DIR, 'custom_dir' ),
+			'baseurl' => 'http://example.com/custom-path/fonts/my-custom-dir',
 			'error'   => false,
 		);
 
@@ -69,4 +76,113 @@ function set_new_values( $defaults ) {
 
 		$this->assertSame( static::$dir_defaults, $font_dir, 'The wp_get_font_dir() method should return the default values.' );
 	}
+
+	public function test_non_writable_filtered_dir() {
+		// Define a callback function to pass to the filter.
+		function set_custom_dir( $defaults ) {
+			$defaults['path']    = path_join( WP_CONTENT_DIR, 'custom_dir' );
+			$defaults['url']     = 'http://example.com/custom-path/fonts/my-custom-dir';
+			$defaults['basedir'] = path_join( WP_CONTENT_DIR, 'custom_dir' );
+			$defaults['baseurl'] = 'http://example.com/custom-path/fonts/my-custom-dir';
+			return $defaults;
+		}
+
+		// Add the filter.
+		add_filter( 'font_dir', 'set_custom_dir' );
+
+		// make 'wp-content/custom_dir' non-writable
+		$this->create_fake_file_to_avoid_dir_creation( path_join( WP_CONTENT_DIR, 'custom_dir' ) );
+
+		// Gets the fonts dir.
+		$font_dir = wp_get_font_dir();
+
+		$expected = array(
+			'path'    => path_join( WP_CONTENT_DIR, 'custom_dir' ),
+			'url'     => 'http://example.com/custom-path/fonts/my-custom-dir',
+			'subdir'  => '',
+			'basedir' => path_join( WP_CONTENT_DIR, 'custom_dir' ),
+			'baseurl' => 'http://example.com/custom-path/fonts/my-custom-dir',
+			'error'   => 'Unable to create directory wp-content/custom_dir. Is its parent directory writable by the server?',
+		);
+
+		$this->assertSame( $expected, $font_dir, 'The wp_get_font_dir() method should return the filtered values with an error message.' );
+	}
+
+	public function test_should_create_fonts_dir_in_uploads_when_fails_in_wp_content() {
+		// Set the expected results.
+		$upload_dir = wp_upload_dir();
+		$expected   = array(
+			'path'    => path_join( $upload_dir['basedir'], 'fonts' ),
+			'url'     => $upload_dir['baseurl'] . '/fonts',
+			'subdir'  => '',
+			'basedir' => path_join( $upload_dir['basedir'], 'fonts' ),
+			'baseurl' => $upload_dir['baseurl'] . '/fonts',
+			'error'   => false,
+		);
+
+		$this->create_fake_file_to_avoid_dir_creation( static::$dir_defaults['path'] );
+		$this->assertFileExists( static::$dir_defaults['path'] );
+
+		$font_dir = wp_get_font_dir();
+
+		$this->assertDirectoryDoesNotExist( static::$dir_defaults['path'], 'The `wp-content/fonts` directory should not exist.' );
+		$this->assertDirectoryExists( $font_dir['path'], 'The `uploads/fonts` directory should exist.' );
+		$this->assertSame( $expected, $font_dir, 'The `fonts` directory should be a subdir in the `uploads` directory.' );
+	}
+
+	public function test_should_return_error_if_unable_to_create_fonts_dir_in_uploads() {
+		// Disallow the creation of the `wp-content/fonts` directory.
+		$this->create_fake_file_to_avoid_dir_creation( static::$dir_defaults['path'] );
+		$this->assertFileExists( static::$dir_defaults['path'] );
+
+		// Disallow the creation of the `uploads/fonts` directory.
+		$upload_dir       = wp_upload_dir();
+		$font_upload_path = path_join( $upload_dir['basedir'], 'fonts' );
+		$this->create_fake_file_to_avoid_dir_creation( $font_upload_path );
+		$this->assertFileExists( $font_upload_path );
+
+		$expected = array(
+			'path'    => $font_upload_path,
+			'url'     => $upload_dir['baseurl'] . '/fonts',
+			'subdir'  => '',
+			'basedir' => $font_upload_path,
+			'baseurl' => $upload_dir['baseurl'] . '/fonts',
+			'error'   => 'Unable to create directory wp-content/uploads/fonts. Is its parent directory writable by the server?',
+		);
+
+		$font_dir = wp_get_font_dir();
+
+		$this->assertDirectoryDoesNotExist( $font_upload_path, 'The `uploads/fonts` directory should not exist.' );
+		$this->assertSame( $expected, $font_dir, 'As /wp-content/uplods/fonts is not writable the error key should be populated with an error message.' );
+	}
+
+	private function remove_font_paths() {
+		$paths = array(
+			path_join( WP_CONTENT_DIR, 'fonts' ),
+			path_join( WP_CONTENT_DIR, 'custom_dir' ),
+			path_join( WP_CONTENT_DIR, 'uploads/fonts' ),
+		);
+
+		foreach ( $paths as $path ) {
+			if ( ! is_dir( $path ) ) {
+				if ( file_exists( $path ) ) {
+					unlink( $path );
+				}
+			} else {
+				$this->rmdir( $path );
+				rmdir( $path );
+			}
+		}
+	}
+
+	/**
+	 * A placeholder "fake" file at $path triggers `wp_mkdir_p()` to fail into the `file_exists()` bail out, causing `is_dir()` to  return `false`.
+	 * This effectively makes $path unwritable.
+	 */
+	private function create_fake_file_to_avoid_dir_creation( $path ) {
+		file_put_contents(
+			$path,
+			'fake file'
+		);
+	}
 }