diff --git a/src/core/org/luaj/lib/CoroutineLib.java b/src/core/org/luaj/lib/CoroutineLib.java
index b1f8346b..20e49e23 100644
--- a/src/core/org/luaj/lib/CoroutineLib.java
+++ b/src/core/org/luaj/lib/CoroutineLib.java
@@ -85,12 +85,12 @@ public class CoroutineLib extends LFunction {
 				break;
 			}
 			case CREATE: {
-				LClosure c = (LClosure) vm.topointer(2);
-				vm.pushlvalue( new LThread(c) );
+				LFunction c = vm.checkfunction(2);
+				vm.pushlvalue( new LThread( c, c.luaGetEnv(vm._G) ) );
 				break;
 			}
 			case RESUME: {
-				LThread t = (LThread) vm.topointer(2);
+				LThread t = vm.checkthread(2);
 				t.resumeFrom( vm, vm.gettop()-2 );
 				return false;
 			}
@@ -104,12 +104,12 @@ public class CoroutineLib extends LFunction {
 				break;
 			}
 			case STATUS: {
-				vm.pushstring( ((LThread) vm.topointer(2)).getStatus() );
+				vm.pushstring( vm.checkthread(2).getStatus() );
 				break;
 			}
 			case WRAP: {
-				LClosure c = (LClosure) vm.topointer(2);
-				vm.pushlvalue( new CoroutineLib(WRAPPED,new LThread(c)) );
+				LFunction c = vm.checkfunction(2);
+				vm.pushlvalue( new CoroutineLib(WRAPPED,new LThread(c, c.luaGetEnv(vm._G))) );
 				break;
 			}
 			case YIELD: {
diff --git a/src/core/org/luaj/lib/PackageLib.java b/src/core/org/luaj/lib/PackageLib.java
index 7ace4c0d..0844e183 100644
--- a/src/core/org/luaj/lib/PackageLib.java
+++ b/src/core/org/luaj/lib/PackageLib.java
@@ -126,9 +126,7 @@ public class PackageLib extends LFunction {
 			loadlib(vm);
 			break;
 		case SEEALL: { 
-			if ( ! vm.istable(2) )
-				vm.error( "table expected, got "+vm.typename(2) );
-			LTable t = vm.totable(2);
+			LTable t = vm.checktable(2);
 			LTable m = t.luaGetMetatable();
 			if ( m == null )
 				t.luaSetMetatable(m = new LTable());
@@ -178,7 +176,7 @@ public class PackageLib extends LFunction {
 	 * each option is a function to be applied over the module.
 	 */
 	public static void module(LuaState vm) {
-		LString modname = vm.tolstring(2);
+		LString modname = vm.checklstring(2);
 		int n = vm.gettop();
 		LValue value = LOADED.get(modname);
 		LTable module;
@@ -277,7 +275,7 @@ public class PackageLib extends LFunction {
 	 * the module, then require signals an error.
 	 */	
 	public void require( LuaState vm ) {
-		LString name = vm.tolstring(2);
+		LString name = vm.checklstring(2);
 		LValue loaded = LOADED.get(name);
 		if ( loaded.toJavaBoolean() ) {
 			if ( loaded == _SENTINEL )
diff --git a/src/core/org/luaj/vm/LClosure.java b/src/core/org/luaj/vm/LClosure.java
index 2415a0fa..e93ee0e7 100644
--- a/src/core/org/luaj/vm/LClosure.java
+++ b/src/core/org/luaj/vm/LClosure.java
@@ -53,4 +53,10 @@ public class LClosure extends LFunction {
 		this.env = t;
 		return 1;
 	}
+
+	/** Get the enviroment for this closure */
+	public LTable luaGetEnv(LTable d) {
+		return env;
+	}
+
 }
diff --git a/src/core/org/luaj/vm/LFunction.java b/src/core/org/luaj/vm/LFunction.java
index e2ba54f3..0ae88ad4 100644
--- a/src/core/org/luaj/vm/LFunction.java
+++ b/src/core/org/luaj/vm/LFunction.java
@@ -37,6 +37,18 @@ public class LFunction extends LValue {
 		return Lua.LUA_TFUNCTION;
 	}
 
+	/**
+	 * Get the environment of the object if it is a closure, or d if not a closure.
+	 * 
+	 * @param d global environment 
+	 * @return environment for this object, or d if it is not an LClosure
+	 * @see LClosure
+	 * @see LTable
+	 */
+	public LTable luaGetEnv(LTable d) {
+		return d;
+	}
+	
 	/**
 	 * Set up a Java invocation, and leave the results on the stack 
 	 * starting at base.  The default implementation for LFunction
@@ -91,5 +103,6 @@ public class LFunction extends LValue {
 	public void __newindex(LuaState vm, LValue table, LValue key, LValue val) {
 		vm.call(this, table, key, val);
 	}
+
 	
 }
diff --git a/src/core/org/luaj/vm/LThread.java b/src/core/org/luaj/vm/LThread.java
index 8ab03492..95feddac 100644
--- a/src/core/org/luaj/vm/LThread.java
+++ b/src/core/org/luaj/vm/LThread.java
@@ -46,8 +46,8 @@ public class LThread extends LValue implements Runnable {
 	static LThread running;
 	
 	
-	public LThread(LClosure c) {
-		threadVm = new LuaState(c.env);
+	public LThread(LFunction c, LTable env) {
+		threadVm = new LuaState(env);
 		threadVm.pushlvalue(c);
 	}
 
diff --git a/src/core/org/luaj/vm/LuaState.java b/src/core/org/luaj/vm/LuaState.java
index 02023e6b..c03f099d 100644
--- a/src/core/org/luaj/vm/LuaState.java
+++ b/src/core/org/luaj/vm/LuaState.java
@@ -2680,6 +2680,18 @@ public class LuaState extends Lua {
 		return (LFunction) checktype(narg, Lua.LUA_TFUNCTION);
 	}
 	
+	/**
+	 * Checks whether the function argument <code>narg</code> is a thread and
+	 * returns this thread.
+	 * @see LThread
+	 * @param narg the argument number
+	 * @throws LuaErrorException if the value is not a thread
+	 * @return LThread value if the argument is a thread
+	 */
+	public LThread checkthread(int narg) {
+		return (LThread) checktype(narg, Lua.LUA_TTHREAD);
+	}
+	
 	/**
 	 * Checks whether the function argument <code>narg</code> is a number and
 	 * returns this number cast to an <code>int</code>.