diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 198bf94478..2fb98bcb9d 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -934,7 +934,10 @@ function get_theme_mod( $name, $default = false ) {
 	}
 
 	if ( is_string( $default ) ) {
-		$default = sprintf( $default, get_template_directory_uri(), get_stylesheet_directory_uri() );
+		// Only run the replacement if an sprintf() string format pattern was found.
+		if ( preg_match( '#(?<!%)%(?:\d+\$?)?s#', $default ) ) {
+			$default = sprintf( $default, get_template_directory_uri(), get_stylesheet_directory_uri() );
+		}
 	}
 
 	/** This filter is documented in wp-includes/theme.php */
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 2da00ea211..89a4d056ba 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-beta2-46394';
+$wp_version = '5.3-beta2-46395';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.