diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/TypeTightener.java b/dev/core/src/com/google/gwt/dev/jjs/impl/TypeTightener.java
index 9162ede..7d9b5de 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/impl/TypeTightener.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/TypeTightener.java
@@ -473,7 +473,10 @@
 
     @Override
     public void exit(JField x, Context ctx) {
-      if (program.codeGenTypes.contains(x.getEnclosingType())) {
+      // TODO: we should also skip @JsType fields when we implement them.
+      if (program.codeGenTypes.contains(x.getEnclosingType())
+          || program.typeOracle.isExportedField(x)) {
+        // We cannot tighten this field as we don't know all callers.
         return;
       }
       if (!x.isVolatile()) {
@@ -659,6 +662,13 @@
 
     @Override
     public void endVisit(JParameter x, Context ctx) {
+      JMethod currentMethod = getCurrentMethod();
+      if (program.codeGenTypes.contains(currentMethod.getEnclosingType())
+          || program.typeOracle.isExportedMethod(currentMethod)
+          || program.typeOracle.isJsTypeMethod(currentMethod)) {
+        // We cannot tighten this parameter as we don't know all callers.
+        return;
+      }
       tighten(x);
     }
 
@@ -684,8 +694,7 @@
        * Explicitly NOT visiting native methods since we can't infer further
        * type information.
        */
-      return !program.codeGenTypes.contains(x.getEnclosingType()) && !x.isNative()
-          || program.typeOracle.isJsTypeMethod(x) || program.typeOracle.isExportedMethod(x);
+      return !x.isNative();
     }
 
     /**
@@ -734,10 +743,6 @@
       }
       JReferenceType refType = (JReferenceType) x.getType();
 
-      if (program.typeOracle.isJsType(refType)) {
-        return;
-      }
-
       if (refType == program.getTypeNull()) {
         return;
       }
diff --git a/user/test/com/google/gwt/core/client/interop/JsTypeTest.java b/user/test/com/google/gwt/core/client/interop/JsTypeTest.java
index 3581d6e..7793d50 100644
--- a/user/test/com/google/gwt/core/client/interop/JsTypeTest.java
+++ b/user/test/com/google/gwt/core/client/interop/JsTypeTest.java
@@ -168,6 +168,10 @@
     // Test exported constructor called from JS in module window
     ScriptInjector.fromString("new $wnd.MyClassImpl3();").inject();
     assertTrue(MyClassImpl3.calledFromJsModuleWindow);
+
+    // This is to reproduce the problem where we incorrectly type-tighten an exported method params.
+    ScriptInjector.fromString("$wnd.MyClassImpl3.foo($wnd.newA());").inject();
+    assertTrue(MyClassImpl3.calledFromBar);
   }
 
   public void testCasts() {
diff --git a/user/test/com/google/gwt/core/client/interop/MyClassImpl3.java b/user/test/com/google/gwt/core/client/interop/MyClassImpl3.java
index c71640a..b84fde5 100644
--- a/user/test/com/google/gwt/core/client/interop/MyClassImpl3.java
+++ b/user/test/com/google/gwt/core/client/interop/MyClassImpl3.java
@@ -35,4 +35,23 @@
       Assert.assertEquals(42, foo);
       calledFromJsModuleWindow = true;
   }
+
+  public static boolean calledFromBar = false;
+
+  public static class A {
+    void bar() {
+      calledFromBar = true;
+    }
+  }
+
+  // There should be no calls to this method from java.
+  @JsExport("$wnd.MyClassImpl3.foo")
+  public static void foo(A a) {
+    a.bar();
+  }
+
+  @JsExport("$wnd.newA")
+  private static A newA() {
+    return new A();
+  }
 }