diff --git a/wp-includes/compat.php b/wp-includes/compat.php
index 4448708df..38a6652cf 100644
--- a/wp-includes/compat.php
+++ b/wp-includes/compat.php
@@ -98,18 +98,37 @@ if (!function_exists('array_change_key_case')) {
 		}
 }
 
-// From php.net
-if(!function_exists('http_build_query')) {
-	 function http_build_query( $formdata, $numeric_prefix = null, $key = null ) {
-			 $res = array();
-			 foreach ((array)$formdata as $k=>$v) {
-					 $tmp_key = urlencode(is_int($k) ? $numeric_prefix.$k : $k);
-					 if ($key) $tmp_key = $key.'['.$tmp_key.']';
-					 $res[] = ( ( is_array($v) || is_object($v) ) ? http_build_query($v, null, $tmp_key) : $tmp_key."=".urlencode($v) );
-			 }
-			 $separator = ini_get('arg_separator.output');
-			 return implode($separator, $res);
-	 }
+if (!function_exists('http_build_query')) {
+	function http_build_query($data, $prefix=null, $sep=null) {
+		return _http_build_query($data, $prefix, $sep);
+	}
+}
+
+// from php.net (modified by Mark Jaquith to behave like the native PHP5 function)
+function _http_build_query($data, $prefix=null, $sep=null, $key='') {
+	$ret = array();
+	foreach ( (array) $data as $k => $v ) {
+		$k = urlencode($k);
+		if ( is_int($k) && $prefix != null )
+			$k = $prefix.$k;
+		if ( !empty($key) )
+			$k = $key . '%5B' . $k . '%5D';
+
+		if ( $v === NULL )
+			continue;
+		elseif ( $v === FALSE )
+			$v = '0';
+
+		if ( is_array($v) || is_object($v) )
+			array_push($ret,_http_build_query($v, '', $sep, $k));
+		else
+			array_push($ret, $k.'='.urlencode($v));
+		}
+
+	if ( NULL === $sep )
+		$sep = ini_get('arg_separator.output');
+
+	return implode($sep, $ret);
 }
 
 if ( !function_exists('_') ) {
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index fdbfefdf1..3a95d0128 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -644,17 +644,17 @@ function add_query_arg() {
 		$qs[func_get_arg(0)] = func_get_arg(1);
 	}
 
-	foreach($qs as $k => $v) {
-		if ( $v !== FALSE ) {
-			if ( $ret != '' )
-				$ret .= '&';
-			if ( empty($v) && !preg_match('|[?&]' . preg_quote($k, '|') . '=|', $query) )
-				$ret .= $k;
-			else
-				$ret .= "$k=$v";
-		}
+	foreach ( $qs as $k => $v ) {
+		if ( $v === false )
+			unset($qs[$k]);
 	}
+
+	if ( ini_get('arg_separator.output') === '&')
+		$ret = http_build_query($qs, '', '&');
+	else
+		$ret = _http_build_query($qs, NULL, '&');
 	$ret = trim($ret, '?');
+	$ret = preg_replace('#=(&|$)#', '$1', $ret);
 	$ret = $protocol . $base . $ret . $frag;
 	$ret = rtrim($ret, '?');
 	return $ret;