diff --git a/src/core/org/luaj/vm2/LuaValue.java b/src/core/org/luaj/vm2/LuaValue.java
index 4dadb235..42d3627a 100644
--- a/src/core/org/luaj/vm2/LuaValue.java
+++ b/src/core/org/luaj/vm2/LuaValue.java
@@ -161,11 +161,11 @@ public class LuaValue extends Varargs {
 	
 	// errors
 	public static LuaValue error(String message) { throw new LuaError(message); }
-	public static LuaValue error(int iarg, String message) { throw new LuaError("arg "+iarg+": "+message); }
+	public static LuaValue error(int iarg, String message) { throw new LuaError("bad argument #"+iarg+": "+message); }
 	public static void assert_(boolean b,String msg) { if(!b) throw new LuaError(msg); }
-	public static void argerror(int i,String msg) { throw new LuaError("arg "+i+": "+msg); }
+	public static void argerror(int iarg,String msg) { throw new LuaError("bad argument #"+iarg+": "+msg); }
 	protected LuaValue typerror(String expected) { throw new LuaError(expected+" expected, got "+typename()); }
-	protected LuaValue typerror(int iarg, String expected) { throw new LuaError("arg "+iarg+": "+expected+" expected, got "+typename()); }
+	protected LuaValue typerror(int iarg, String expected) { throw new LuaError("bad argument #"+iarg+": "+expected+" expected, got "+typename()); }
 	protected LuaValue unimplemented(String fun) { throw new LuaError("'"+fun+"' not implemented for "+typename()); }
 	protected LuaValue aritherror() { throw new LuaError("attempt to perform arithmetic on "+typename()); }
 	protected LuaValue aritherror(String fun) { throw new LuaError("attempt to perform arithmetic '"+fun+"' on "+typename()); }
diff --git a/src/core/org/luaj/vm2/lib/BaseLib.java b/src/core/org/luaj/vm2/lib/BaseLib.java
index 0e888dad..8e0b40e0 100644
--- a/src/core/org/luaj/vm2/lib/BaseLib.java
+++ b/src/core/org/luaj/vm2/lib/BaseLib.java
@@ -153,19 +153,20 @@ public class BaseLib extends OneArgFunction implements ResourceFinder {
 		public LuaValue call(LuaValue arg1, LuaValue arg2) {
 			switch ( opcode ) {
 			case 0: // "collectgarbage", // ( opt [,arg] ) -> value
-				String s = arg1.optjstring("collect");
+				String s = arg1.checkjstring();
 				int result = 0;
 				if ( "collect".equals(s) ) {
 					System.gc();
 					return ZERO;
-				}
-				else if ( "count".equals(s) ) {
+				} else if ( "count".equals(s) ) {
 					Runtime rt = Runtime.getRuntime();
 					long used = rt.totalMemory() - rt.freeMemory();
 					return valueOf(used/1024.);
 				} else if ( "step".equals(s) ) {
 					System.gc();
 					return LuaValue.TRUE;
+				} else {
+					this.argerror(1, "gc op");
 				}
 				return NIL;
 			case 1: // "error", // ( message [,level] ) -> ERR
diff --git a/test/lua/errors/baselibargs.lua b/test/lua/errors/baselibargs.lua
index 60c07b2f..77ac43e6 100644
--- a/test/lua/errors/baselibargs.lua
+++ b/test/lua/errors/baselibargs.lua
@@ -12,7 +12,8 @@ checkallerrors('assert',{{nil,false,n=2},{'message'}},'message')
 -- collectgarbage
 banner('collectgarbage')
 checkallpass('collectgarbage',{{'collect','count'}},true)
-checkallerrors('collectgarbage',{notanil},'bad argument #1')
+checkallerrors('collectgarbage',{{astring, anumber}},'bad argument #1')
+checkallerrors('collectgarbage',{{aboolean, atable, afunction, athread}},'string expected')
 
 -- dofile
 banner('dofile')