diff --git a/engines/LuaStandalone/LuaStandaloneEngine.php b/engines/LuaStandalone/LuaStandaloneEngine.php
index f694cc20..ecec1762 100644
--- a/engines/LuaStandalone/LuaStandaloneEngine.php
+++ b/engines/LuaStandalone/LuaStandaloneEngine.php
@@ -174,6 +174,7 @@ class Scribunto_LuaStandaloneInterpreter extends Scribunto_LuaInterpreter {
 		$result = $this->dispatch( array(
 			'op' => 'call',
 			'id' => $func->id,
+			'nargs' => count( $args ),
 			'args' => $args ) );
 		// Convert return values to zero-based
 		return array_values( $result );
@@ -212,7 +213,23 @@ class Scribunto_LuaStandaloneInterpreter extends Scribunto_LuaInterpreter {
 		return $result[1];
 	}
 
+	/**
+	 * Fill in missing nulls in a list received from Lua
+	 *
+	 * @param $array array List received from Lua
+	 * @param $count integer Number of values that should be in the list
+	 * @return array Non-sparse array
+	 */
+	private static function fixNulls( array $array, $count ) {
+		if ( count( $array ) === $count ) {
+			return $array;
+		} else {
+			return array_replace( array_fill( 1, $count, null ), $array );
+		}
+	}
+
 	protected function handleCall( $message ) {
+		$message['args'] = self::fixNulls( $message['args'], $message['nargs'] );
 		try {
 			$result = $this->callback( $message['id'], $message['args'] );
 		} catch ( Scribunto_LuaError $e ) {
@@ -230,6 +247,7 @@ class Scribunto_LuaStandaloneInterpreter extends Scribunto_LuaInterpreter {
 
 		return array(
 			'op' => 'return',
+			'nvalues' => count( $result ),
 			'values' => $result
 		);
 	}
@@ -258,7 +276,7 @@ class Scribunto_LuaStandaloneInterpreter extends Scribunto_LuaInterpreter {
 
 			switch ( $msgFromLua['op'] ) {
 				case 'return':
-					return $msgFromLua['values'];
+					return self::fixNulls( $msgFromLua['values'], $msgFromLua['nvalues'] );
 				case 'call':
 					$msgToLua = $this->handleCall( $msgFromLua );
 					$this->sendMessage( $msgToLua );
diff --git a/engines/LuaStandalone/MWServer.lua b/engines/LuaStandalone/MWServer.lua
index d0199c38..962bd36b 100644
--- a/engines/LuaStandalone/MWServer.lua
+++ b/engines/LuaStandalone/MWServer.lua
@@ -34,21 +34,28 @@ function MWServer:execute()
 	self:debug( 'MWServer:execute: returning' )
 end
 
+-- Convert a multiple-return-value or a ... into a count and a table
+function MWServer:listToCountAndTable( ... )
+	return select( '#', ... ), { ... }
+end
+
 --- Call a PHP function
 -- Raise an error if the PHP handler requests it. May return any number
 -- of values.
 --
 -- @param id The function ID, specified by a registerLibrary message
+-- @param nargs Count of function arguments
 -- @param args The function arguments
 -- @return The return values from the PHP function
-function MWServer:call( id, args )
+function MWServer:call( id, nargs, args )
 	local result = self:dispatch( {
 		op = 'call',
 		id = id,
+		nargs = nargs,
 		args = args
 	} )
 	if result.op == 'return' then
-		return unpack( result.values )
+		return unpack( result.values, 1, result.nvalues )
 	elseif result.op == 'error' then
 		-- Raise an error in the actual user code that called the function
 		-- The level is 3 since our immediate caller is a closure
@@ -63,19 +70,22 @@ end
 -- @param message The message from PHP
 -- @return A response message to send back to PHP
 function MWServer:handleCall( message )
-	local result = { xpcall( 
+	local n, result = self:listToCountAndTable( xpcall(
 		function ()
-			return self.chunks[message.id]( unpack( message.args ) )
+			return self.chunks[message.id]( unpack( message.args, 1, message.nargs ) )
 		end,
 		function ( err )
 			return MWServer:attachTrace( err )
-		end 
-		) }
-	
+		end
+	) )
+
 	if result[1] then
-		table.remove( result, 1 )
+		-- table.remove( result, 1 ) renumbers from 2 to #result. But #result
+		-- is not necessarily "right" if result contains nils.
+		result = { unpack( result, 2, n ) }
 		return {
 			op = 'return',
+			nvalues = n - 1,
 			values = result
 		}
 	else
@@ -124,6 +134,7 @@ function MWServer:handleLoadString( message )
 		local id = self:addChunk( chunk )
 		return {
 			op = 'return',
+			nvalues = 1,
 			values = {id}
 		}
 	else
@@ -161,14 +172,15 @@ function MWServer:handleRegisterLibrary( message )
 
 	for name, id in pairs( message.functions ) do
 		t[name] = function( ... )
-			return self:call( id, { ... } )
+			return self:call( id, self:listToCountAndTable( ... ) )
 		end
 		-- Protect the function against setfenv()
 		self.protectedFunctions[t[name]] = true
 	end
-	
+
 	return {
 		op = 'return',
+		nvalues = 0,
 		values = {}
 	}
 end
@@ -181,13 +193,14 @@ end
 function MWServer:handleWrapPhpFunction( message )
 	local id = message.id
 	local func = function( ... )
-		return self:call( id, { ... } )
+		return self:call( id, self:listToCountAndTable( ... ) )
 	end
 	-- Protect the function against setfenv()
 	self.protectedFunctions[func] = true
 
 	return {
 		op = 'return',
+		nvalues = 1,
 		values = { func }
 	}
 end
@@ -199,6 +212,7 @@ end
 function MWServer:handleGetStatus( message )
 	local nullRet = {
 		op = 'return',
+		nvalues = 0,
 		values = {}
 	}
 	local file = io.open( '/proc/self/stat' )
@@ -216,6 +230,7 @@ function MWServer:handleGetStatus( message )
 	end
 	return {
 		op = 'return',
+		nvalues = 1,
 		values = {{
 			pid = tonumber(t[1]),
 			time = tonumber(t[14]) + tonumber(t[15]) + tonumber(t[16]) + tonumber(t[17]),
diff --git a/engines/LuaStandalone/protocol.txt b/engines/LuaStandalone/protocol.txt
index edaf2249..157383d5 100644
--- a/engines/LuaStandalone/protocol.txt
+++ b/engines/LuaStandalone/protocol.txt
@@ -22,7 +22,8 @@ message. In this way, a stack of pending requests can be accumulated. This
 mechanism allows re-entrant and recursive calls. 
 
 All numerically-indexed arrays should start from index 1 unless otherwise
-specified.
+specified. Note that the number of values in an array may not match what Lua's
+'#' operator returns if the array contains nils.
 
 == Request messages sent from PHP to Lua ==
 
@@ -38,6 +39,7 @@ Message parameters:
 On success, the response message is:
 
 * op: "return"
+* nvalues: 1
 * values: An array with a single element with the ID in it
 
 On failure, the response message is:
@@ -52,11 +54,13 @@ Call a Lua function.
 Message parameters:
 * op: "call"
 * id: The chunk ID
+* nargs: Number of arguments, including nils
 * args: The argument array
 
 On success, the response message is:
 
 * op: "return"
+* nvalues: Number of return values, including nils
 * values: All return values as an array
 
 On failure, the response message is:
@@ -81,6 +85,7 @@ Message parameters:
 On success, the response message is:
 
 * op: "return"
+* nvalues: 0
 * values: An empty array
 
 On failure the response message is:
@@ -98,6 +103,7 @@ Message parameters:
 On success, the response message is:
 
 * op: "return"
+* nvalues: 1
 * values: An array with a single element, which is an associative array mapping
   status key to value. The status keys are:
 ** pid: The process identifier
@@ -108,6 +114,7 @@ On success, the response message is:
 On failure, the response message is:
 
 * op: "return"
+* nvalues: 0
 * values: An empty array
 
 === quit ===
@@ -128,11 +135,13 @@ Call a PHP function.
 Message parameters:
 * op: "call"
 * id: The function ID given by registerLibrary
+* nargs: Number of arguments, including nils
 * args: An array giving the function arguments
 
 On success, the response message is:
 
 * op: "return"
+* nvalues: Number of return values, including nils
 * values: All return values as an array
 
 On failure the response message is:
diff --git a/tests/engines/LuaCommon/LuaInterpreterTest.php b/tests/engines/LuaCommon/LuaInterpreterTest.php
index 5c831c79..4a532ba4 100644
--- a/tests/engines/LuaCommon/LuaInterpreterTest.php
+++ b/tests/engines/LuaCommon/LuaInterpreterTest.php
@@ -108,6 +108,10 @@ abstract class Scribunto_LuaInterpreterTest extends MediaWikiTestCase {
 			array( array( 'x' => 'foo', 'y' => 'bar', 'z' => array() ) ),
 			array( INF ),
 			array( -INF ),
+			array( 'ok', null, 'ok' ),
+			array( null, 'ok' ),
+			array( 'ok', null ),
+			array( null ),
 		);
 	}