--- ../src-base/minecraft/net/minecraft/util/MouseHelper.java
+++ ../src-work/minecraft/net/minecraft/util/MouseHelper.java
@@ -14,6 +14,7 @@
 
     public void func_74372_a()
     {
+        if (Boolean.parseBoolean(System.getProperty("fml.noGrab","false"))) return;
         Mouse.setGrabbed(true);
         this.field_74377_a = 0;
         this.field_74375_b = 0;
