diff --git a/wp-includes/compat.php b/wp-includes/compat.php
index 553faeb1d8..b2308e8f22 100644
--- a/wp-includes/compat.php
+++ b/wp-includes/compat.php
@@ -260,3 +260,59 @@ endif;
 if ( ! defined( 'JSON_PRETTY_PRINT' ) ) {
 	define( 'JSON_PRETTY_PRINT', 128 );
 }
+
+if ( ! function_exists( 'json_last_error_msg' ) ) :
+	/**
+	 * Retrieves the error string of the last json_encode() or json_decode() call.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @internal This is a compatibility function for PHP <5.5
+	 *
+	 * @return bool|string Returns the error message on success, "No Error" if no error has occurred,
+	 *                     or false on failure.
+	 */
+	function json_last_error_msg() {
+		// See https://core.trac.wordpress.org/ticket/27799.
+		if ( ! function_exists( 'json_last_error' ) ) {
+			return false;
+		}
+
+		$last_error_code = json_last_error();
+
+		// Just in case JSON_ERROR_NONE is not defined.
+		$error_code_none = defined( 'JSON_ERROR_NONE' ) ? JSON_ERROR_NONE : 0;
+
+		switch ( true ) {
+			case $last_error_code === $error_code_none:
+				return 'No error';
+
+			case defined( 'JSON_ERROR_DEPTH' ) && JSON_ERROR_DEPTH === $last_error_code:
+				return 'Maximum stack depth exceeded';
+
+			case defined( 'JSON_ERROR_STATE_MISMATCH' ) && JSON_ERROR_STATE_MISMATCH === $last_error_code:
+				return 'State mismatch (invalid or malformed JSON)';
+
+			case defined( 'JSON_ERROR_CTRL_CHAR' ) && JSON_ERROR_CTRL_CHAR === $last_error_code:
+				return 'Control character error, possibly incorrectly encoded';
+
+			case defined( 'JSON_ERROR_SYNTAX' ) && JSON_ERROR_SYNTAX === $last_error_code:
+				return 'Syntax error';
+
+			case defined( 'JSON_ERROR_UTF8' ) && JSON_ERROR_UTF8 === $last_error_code:
+				return 'Malformed UTF-8 characters, possibly incorrectly encoded';
+
+			case defined( 'JSON_ERROR_RECURSION' ) && JSON_ERROR_RECURSION === $last_error_code:
+				return 'Recursion detected';
+
+			case defined( 'JSON_ERROR_INF_OR_NAN' ) && JSON_ERROR_INF_OR_NAN === $last_error_code:
+				return 'Inf and NaN cannot be JSON encoded';
+
+			case defined( 'JSON_ERROR_UNSUPPORTED_TYPE' ) && JSON_ERROR_UNSUPPORTED_TYPE === $last_error_code:
+				return 'Type is not supported';
+
+			default:
+				return 'An unknown error occurred';
+		}
+	}
+endif;
\ No newline at end of file
diff --git a/wp-includes/version.php b/wp-includes/version.php
index ed98731b9f..4d9fb49055 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34843';
+$wp_version = '4.4-alpha-34844';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.