diff -r 93e0a19c805a -r 0206df35882c jitcraft/BytecodeCompiler.cpp
--- a/jitcraft/BytecodeCompiler.cpp	Tue Jul 17 03:59:52 2012 -0700
+++ b/jitcraft/BytecodeCompiler.cpp	Tue Jul 17 21:40:44 2012 -0700
@@ -49,6 +49,10 @@
         BinaryExpression *b = expr->toBinaryExpression();
         if (b->token() >= TOK_EQUALS && b->token() <= TOK_OR)
             return b->token();
+    } else if (expr->isUnaryExpression()) {
+        UnaryExpression *u = expr->toUnaryExpression();
+        if (u->token() == TOK_NOT)
+            return TOK_NOT;
     }
     return TOK_EOF;
 }
@@ -404,6 +408,18 @@
 BytecodeCompiler::visit(UnaryExpression *node)
 {
     switch (node->token()) {
+      case TOK_NOT:
+      {
+        Local<Type> type(zone_, node->expression()->type());
+        node->expression()->accept(this);
+        
+        if (node->type()->isFloat())
+            __ not_f();
+        else
+            __ not_();
+        break;
+      }
+
       default:
         assert(node->token() == TOK_TILDE);
         node->expression()->accept(this);
@@ -475,17 +491,22 @@
                                Label *fallthrough)
 {
     TokenKind token = ToCompare(expression);
-    if (token == TOK_EOF) {
-        expression->accept(this);
+    if (token == TOK_EOF || token == TOK_NOT) {
+        if (token == TOK_EOF)
+            expression->accept(this);
+        else
+            expression->toUnaryExpression()->expression()->accept(this);
+        
+        bool jumpOnTrue = (fallthrough == falseBranch) ^ (token == TOK_NOT);
 
-        Opcode op = (fallthrough == trueBranch) ? OP_JF : OP_JT;
+        Opcode op = jumpOnTrue ? OP_JT : OP_JF;
         if (expression->type()->isFloat())
             op = (Opcode)(int(op) + (OP_JL_F - OP_JL));
 
-        if (fallthrough == trueBranch)
-            __ j(op, falseBranch);
+        if (fallthrough == falseBranch)
+            __ j(op, trueBranch);
         else
-            __ j(op, trueBranch);
+            __ j(op, falseBranch); 
         return;
     }