diff --git a/src/core/org/luaj/vm2/LuaClosure.java b/src/core/org/luaj/vm2/LuaClosure.java
index 4b7088bb..df59c8e0 100644
--- a/src/core/org/luaj/vm2/LuaClosure.java
+++ b/src/core/org/luaj/vm2/LuaClosure.java
@@ -236,14 +236,14 @@ public class LuaClosure extends LuaFunction {
 					b = i>>>23;
 					c = (i>>14)&0x1ff;
 					{
-						LuaValue r = stack[c-1].concat(stack[c]);
-						if ( (c-=2) >= b ) {
-							Buffer sb = r.buffer();
-							while ( c>=b )
-								sb = stack[c--].concat(sb);
-							r = sb.value();
+						if ( c > b+1 ) {
+							Buffer sb = stack[c].buffer();
+							while ( --c>=b ) 
+								sb = stack[c].concat(sb);
+							stack[a] = sb.value();
+						} else {
+							stack[a] = stack[c-1].concat(stack[c]);
 						}
-						stack[a] = r;
 					}
 					continue;
 					
diff --git a/src/core/org/luaj/vm2/LuaNumber.java b/src/core/org/luaj/vm2/LuaNumber.java
index aa3d1632..878b7a0c 100644
--- a/src/core/org/luaj/vm2/LuaNumber.java
+++ b/src/core/org/luaj/vm2/LuaNumber.java
@@ -64,6 +64,7 @@ public class LuaNumber extends LuaValue {
 
 	public LuaValue concat(LuaValue rhs)      { return rhs.concatTo(this); }
 	public Buffer   concat(Buffer rhs)        { return rhs.prepend(this.strvalue()); }
+	public LuaValue concatTo(LuaValue lhs)    { return lhs.concaterror(); }
 	public LuaValue concatTo(LuaNumber lhs)   { return strvalue().concatTo(lhs.strvalue()); }
 	public LuaValue concatTo(LuaString lhs)   { return strvalue().concatTo(lhs); }
 
diff --git a/src/core/org/luaj/vm2/LuaString.java b/src/core/org/luaj/vm2/LuaString.java
index 0d8a596b..94085dc2 100644
--- a/src/core/org/luaj/vm2/LuaString.java
+++ b/src/core/org/luaj/vm2/LuaString.java
@@ -157,6 +157,7 @@ public class LuaString extends LuaValue {
 	// concatenation
 	public LuaValue concat(LuaValue rhs)      { return rhs.concatTo(this); }
 	public Buffer   concat(Buffer rhs)        { return rhs.prepend(this); }
+	public LuaValue concatTo(LuaValue lhs)    { return lhs.concaterror(); }
 	public LuaValue concatTo(LuaNumber lhs)   { return concatTo(lhs.strvalue()); }
 	public LuaValue concatTo(LuaString lhs)   { 
 		byte[] b = new byte[lhs.m_length+this.m_length];
diff --git a/src/core/org/luaj/vm2/LuaValue.java b/src/core/org/luaj/vm2/LuaValue.java
index 3cdcaead..38a9265a 100644
--- a/src/core/org/luaj/vm2/LuaValue.java
+++ b/src/core/org/luaj/vm2/LuaValue.java
@@ -179,6 +179,7 @@ public class LuaValue extends Varargs {
 	protected LuaValue aritherror(String fun) { throw new LuaError("attempt to perform arithmetic '"+fun+"' on "+typename()); }
 	protected LuaValue compareerror(String rhs) { throw new LuaError("attempt to compare "+typename()+" with "+rhs); }
 	protected LuaValue compareerror(LuaValue rhs) { throw new LuaError("attempt to compare "+typename()+" with "+rhs.typename()); }
+	protected LuaValue concaterror() { throw new LuaError("attempt to concatenate "+typename()); }
 	
 	// table operations
 	public LuaValue get( LuaValue key ) { return gettable(this,key); }
@@ -344,18 +345,17 @@ public class LuaValue extends Varargs {
 	public int strcmp( LuaString rhs )      { error("attempt to compare "+typename()); return 0; }
 
 	// concatenation
-	public LuaValue concat(LuaValue rhs)      { return this.concatmt(rhs); }
-	public LuaValue concatTo(LuaNumber lhs)   { return lhs.concatmt(this); }
-	public LuaValue concatTo(LuaString lhs)   { return lhs.concatmt(this); }
+	public LuaValue concat(LuaValue rhs)      { return rhs.concatTo(this); }
+	public LuaValue concatTo(LuaValue lhs)    { return lhs.concatmt(this); }
+	public LuaValue concatTo(LuaNumber lhs)   { return concaterror(); }
+	public LuaValue concatTo(LuaString lhs)   { return concaterror(); }
 	public Buffer   buffer()                  { return new Buffer(this); }
-	public Buffer   concat(Buffer rhs)        {
-		return rhs.setvalue(checkmetatag(CONCAT,"attempt to concatenate ").call(this, rhs.value()));
-	}
+	public Buffer   concat(Buffer rhs)        { return rhs.setvalue(concat(rhs.value())); }
 	public LuaValue concatmt(LuaValue rhs) {
 		LuaValue h=metatag(CONCAT);
 		LuaValue v=this;
-		if ( h.isnil() || (h=(v=rhs).metatag(CONCAT)).isnil())
-			v.typerror("attempt to concatenate ");
+		if ( h.isnil() && (h=(v=rhs).metatag(CONCAT)).isnil())
+			return v.concaterror();
 		return h.call(this,rhs);
 	}
 	
diff --git a/test/junit/org/luaj/vm2/UnaryBinaryOperatorsTest.java b/test/junit/org/luaj/vm2/UnaryBinaryOperatorsTest.java
index 2b4ec915..2d19b55e 100644
--- a/test/junit/org/luaj/vm2/UnaryBinaryOperatorsTest.java
+++ b/test/junit/org/luaj/vm2/UnaryBinaryOperatorsTest.java
@@ -25,6 +25,7 @@ import org.luaj.vm2.LuaDouble;
 import org.luaj.vm2.LuaInteger;
 import org.luaj.vm2.LuaString;
 import org.luaj.vm2.LuaValue;
+import org.luaj.vm2.lib.TwoArgFunction;
 
 import junit.framework.TestCase;
 
@@ -646,4 +647,57 @@ public class UnaryBinaryOperatorsTest extends TestCase {
 		b = def.concat(b); assertEquals( "def123", b.value().tojstring() );
 		b = abc.concat(b); assertEquals( "abcdef123", b.value().tojstring() );
 	}
+	
+	public void testConcatMetatag() {
+		LuaValue def = LuaValue.valueOf("abcdefghi").substring(3,6);
+		LuaValue ghi = LuaValue.valueOf("abcdefghi").substring(6,9);
+		LuaValue tru = LuaValue.TRUE;
+		LuaValue fal = LuaValue.FALSE;
+		LuaValue tbl = new LuaTable();
+		LuaValue uda = new LuaUserdata(new Object());
+		try {
+			// always use left argument
+			LuaBoolean.s_metatable = LuaValue.tableOf( new LuaValue[] { 
+					LuaValue.CONCAT, new TwoArgFunction() {
+						public LuaValue call(LuaValue lhs, LuaValue rhs) {
+							return lhs;
+						}
+					} } );
+			assertEquals( tru, tru.concat(tbl) );
+			assertEquals( tbl, tbl.concat(tru) );
+			assertEquals( tru, tru.concat(new Buffer(tbl)).value() );
+			assertEquals( tbl, tbl.concat(new Buffer(tru)).value() );
+			assertEquals( fal, fal.concat(tbl.concat(new Buffer(tru))).value() );
+			assertEquals( uda, uda.concat(tru.concat(new Buffer(tbl))).value() );
+			try { tru.concat(def); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { def.concat(tru); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { tru.concat(new Buffer(def)).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { def.concat(new Buffer(tru)).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { fal.concat(def.concat(new Buffer(tru))).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { ghi.concat(tru.concat(new Buffer(def))).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+
+			// always use right argument
+			LuaBoolean.s_metatable = LuaValue.tableOf( new LuaValue[] { 
+					LuaValue.CONCAT, new TwoArgFunction() {
+						public LuaValue call(LuaValue lhs, LuaValue rhs) {
+							return rhs;
+						}
+					} } );
+			assertEquals( tbl, tru.concat(tbl) );
+			assertEquals( tru, tbl.concat(tru) );
+			assertEquals( tbl, tru.concat(new Buffer(tbl)).value() );
+			assertEquals( tru, tbl.concat(new Buffer(tru)).value() );
+			assertEquals( tru, uda.concat(tbl.concat(new Buffer(tru))).value() );
+			assertEquals( tbl, fal.concat(tru.concat(new Buffer(tbl))).value() );
+			try { tru.concat(def); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { def.concat(tru); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { tru.concat(new Buffer(def)).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { def.concat(new Buffer(tru)).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { uda.concat(def.concat(new Buffer(tru))).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			try { fal.concat(tru.concat(new Buffer(def))).value(); fail("did not throw error"); } catch ( LuaError le ) { };
+			
+		} finally { 
+			LuaBoolean.s_metatable = null;
+		}
+	}
 }