diff --git a/context.ts b/context.ts
index d08abfe0..a800d161 100644
--- a/context.ts
+++ b/context.ts
@@ -191,7 +191,7 @@ module J2ME {
           traceWriter.enter("> " + MethodType[MethodType.Interpreted][0] + " " + frameDetails);
         }
         var returnValue = VM.execute(this);
-        if ($.Y) {
+        if (U) {
           flattenFrameSet();
           return;
         }
@@ -287,16 +287,16 @@ module J2ME {
       this.setCurrent();
       do {
         VM.execute(this);
-        if ($.Y) {
+        if (U) {
           Array.prototype.push.apply(this.frames, this.bailoutFrames);
           this.bailoutFrames = [];
         }
-        if ($.Y === VmState.Yielding) {
+        if (U === VMState.Yielding) {
           // Ignore the yield and continue executing instructions on this thread.
-          $.Y = VmState.Running;
+          U = VMState.Running;
           continue;
-        } else if ($.Y === VmState.Pausing) {
-          $.Y = VmState.Running;
+        } else if (U === VMState.Pausing) {
+          U = VMState.Running;
           Instrument.callPauseHooks(this.current());
           return;
         }
@@ -308,16 +308,16 @@ module J2ME {
       this.setCurrent();
       Instrument.callResumeHooks(ctx.current());
       VM.execute(ctx);
-      if ($.Y) {
+      if (U) {
         Array.prototype.push.apply(this.frames, this.bailoutFrames);
         this.bailoutFrames = [];
       }
-      if ($.Y === VmState.Pausing) {
-        $.Y = VmState.Running;
+      if (U === VMState.Pausing) {
+        U = VMState.Running;
         Instrument.callPauseHooks(this.current());
         return;
       }
-      $.Y = VmState.Running;
+      U = VMState.Running;
       Instrument.callPauseHooks(ctx.current());
 
       if (ctx.frames.length === 0) {
@@ -364,7 +364,7 @@ module J2ME {
       } else {
         while (this.lockLevel-- > 0) {
           this.monitorEnter(obj);
-          if ($.Y === VmState.Pausing) {
+          if (U === VMState.Pausing) {
             return;
           }
         }
diff --git a/interpreter.ts b/interpreter.ts
index 2737009e..3d4b2be4 100644
--- a/interpreter.ts
+++ b/interpreter.ts
@@ -155,7 +155,7 @@ module J2ME {
         return;
       ctx.pushClassInitFrame(classInfo);
 
-      if ($.Y) {
+      if (U) {
         frame.bci = ip;
         return;
       }
@@ -923,7 +923,7 @@ module J2ME {
             if (field.tag)
               field = resolve(idx, true);
             classInitCheck(field.classInfo, frame.bci - 3);
-            if ($.Y) {
+            if (U) {
               return;
             }
             var value = field.getStatic();
@@ -938,7 +938,7 @@ module J2ME {
             if (field.tag)
               field = resolve(idx, true);
             classInitCheck(field.classInfo, frame.bci - 3);
-            if ($.Y) {
+            if (U) {
               return;
             }
             field.setStatic(stack.popType(field.signature));
@@ -949,7 +949,7 @@ module J2ME {
             if (classInfo.tag)
               classInfo = resolve(idx);
             classInitCheck(classInfo, frame.bci - 3);
-            if ($.Y) {
+            if (U) {
               return;
             }
             stack.push(util.newObject(classInfo));
@@ -988,7 +988,7 @@ module J2ME {
               throw ctx.createException("java/lang/NullPointerException");
             }
             ctx.monitorEnter(obj);
-            if ($.Y === VmState.Pausing) {
+            if (U === VMState.Pausing) {
               return;
             }
             break;
@@ -1048,7 +1048,7 @@ module J2ME {
               methodInfo = resolve(idx, isStatic);
               if (isStatic) {
                 classInitCheck(methodInfo.classInfo, startip);
-                if ($.Y) {
+                if (U) {
                   return;
                 }
               }
@@ -1079,7 +1079,7 @@ module J2ME {
             }
 
             var returnValue = fn.apply(obj, args);
-            if ($.Y) {
+            if (U) {
               return;
             }
 
diff --git a/jit/jvm.ir.ts b/jit/jvm.ir.ts
index 993c0e1f..6208533b 100644
--- a/jit/jvm.ir.ts
+++ b/jit/jvm.ir.ts
@@ -520,11 +520,11 @@ module J2ME.C4.Backend {
       var to = id(this.variable.name);
       cx.useVariable(this.variable);
       block.body.push(new AST.ExpressionStatement(assignment(to, result)));
-      var ifYield = new AST.IfStatement(property(id("$"), "Y"), new AST.BlockStatement([
+      var ifUnwind = new AST.IfStatement(id("U"), new AST.BlockStatement([
         new AST.ExpressionStatement(call(property(id("$"), "B"), compileState(this.state, cx))),
         new AST.ReturnStatement(undefined)
       ]));
-      block.body.push(ifYield);
+      block.body.push(ifUnwind);
       return block;
     }
     return result;
diff --git a/jvm.ts b/jvm.ts
index 2b528d2c..b5e3b4e0 100644
--- a/jvm.ts
+++ b/jvm.ts
@@ -21,10 +21,10 @@ module J2ME {
 
       var array = newStringArray(args.length);
       for (var n = 0; n < args.length; ++n)
-        array[n] = args[n] ? util.newString(args[n]) : null;
+        array[n] = args[n] ? J2ME.newString(args[n]) : null;
 
       ctx.frames.push(new Frame(CLASSES.getMethod(isolateClassInfo, "I.<init>.(Ljava/lang/String;[Ljava/lang/String;)V"),
-        [ isolate, util.newString(className.replace(/\./g, "/")), array ], 0));
+        [ isolate, J2ME.newString(className.replace(/\./g, "/")), array ], 0));
       ctx.execute();
 
       ctx.frames.push(new Frame(CLASSES.getMethod(isolateClassInfo, "I.start.()V"), [ isolate ], 0));
@@ -55,7 +55,7 @@ module J2ME {
       ctx.thread.alive = true;
 
       ctx.frames.push(new Frame(CLASSES.getMethod(CLASSES.java_lang_Thread, "I.<init>.(Ljava/lang/String;)V"),
-        [ runtime.mainThread, util.newString("main") ], 0));
+        [ runtime.mainThread, J2ME.newString("main") ], 0));
       var oldCtx = $.ctx;
       ctx.execute();
       oldCtx.setCurrent();
diff --git a/runtime.ts b/runtime.ts
index c0bcc706..180151c3 100644
--- a/runtime.ts
+++ b/runtime.ts
@@ -271,7 +271,7 @@ module J2ME {
       if (internedStrings.has(s)) {
         return internedStrings.get(s);
       }
-      var obj = util.newString(s);
+      var obj = J2ME.newString(s);
       internedStrings.set(s, obj);
       return obj;
     }
@@ -285,7 +285,7 @@ module J2ME {
     }
   }
 
-  export enum VmState {
+  export enum VMState {
     Running = 0,
     Yielding = 1,
     Pausing = 2
@@ -295,11 +295,6 @@ module J2ME {
     private static _nextId: number = 0;
     id: number;
 
-    /**
-     * Are we currently unwinding the stack because of a Yield?
-     */
-    Y: VmState = VmState.Running;
-
     /**
      * Bailout callback whenever a JIT frame is unwound.
      */
@@ -308,11 +303,11 @@ module J2ME {
     }
 
     yield() {
-      this.Y = VmState.Yielding;
+      U = VMState.Yielding;
     }
 
     pause() {
-      this.Y = VmState.Pausing;
+      U = VMState.Pausing;
     }
 
     constructor(jvm: JVM) {
@@ -504,7 +499,7 @@ module J2ME {
         });
         initWriter && initWriter.writeLn("Running Static Constructor: " + classInfo.className);
         $.ctx.pushClassInitFrame(classInfo);
-        assert(!$.Y);
+        assert(!U);
         //// TODO: monitorEnter
         //if (klass.staticInitializer) {
         //  klass.staticInitializer.call(runtimeKlass);
@@ -742,7 +737,7 @@ module J2ME {
             : frame.getLocal(0);
         }
         $.ctx.monitorEnter(frame.lockObject);
-        if ($.Y === VmState.Pausing) {
+        if (U === VMState.Pausing) {
           $.ctx.frames.push(frame);
           return;
         }
@@ -1026,6 +1021,13 @@ module J2ME {
 var Runtime = J2ME.Runtime;
 
 
+/**
+ * Are we currently unwinding the stack because of a Yield? This technically
+ * belonges to a context but we store it in the global object because it is
+ * read very often.
+ */
+var U: J2ME.VMState = J2ME.VMState.Running;
+
 /**
  * Runtime exports for compiled code.
  */