--- old/src/hotspot/share/ci/ciTypeFlow.cpp	2019-03-14 15:03:02.638347903 +0100
+++ new/src/hotspot/share/ci/ciTypeFlow.cpp	2019-03-14 15:03:02.506347397 +0100
@@ -273,6 +273,12 @@
 ciType* ciTypeFlow::StateVector::type_meet_internal(ciType* t1, ciType* t2, ciTypeFlow* analyzer) {
   assert(t1 != t2, "checked in caller");
 
+  // Unwrap the types after gathering nullness information
+  bool never_null1 = t1->is_never_null();
+  bool never_null2 = t2->is_never_null();
+  t1 = t1->unwrap();
+  t2 = t2->unwrap();
+
   if (t1->equals(top_type())) {
     return t2;
   } else if (t2->equals(top_type())) {
@@ -295,12 +301,6 @@
     return bottom_type();
   }
 
-  // Unwrap the types after gathering nullness information
-  bool never_null1 = t1->is_never_null();
-  bool never_null2 = t2->is_never_null();
-  t1 = t1->unwrap();
-  t2 = t2->unwrap();
-
   // Both types are non-top non-primitive types.  That is,
   // both types are either instanceKlasses or arrayKlasses.
   ciKlass* object_klass = analyzer->env()->Object_klass();
@@ -628,10 +628,9 @@
     pop_object();
     do_null_assert(klass);
   } else {
-    pop_object();
-    if (str->is_klass_never_null()) {
+    ciType* type = pop_value();
+    if (klass->is_valuetype() && (str->is_klass_never_null() || type->is_never_null())) {
       // Casting to a Q-Type contains a NULL check
-      assert(klass->is_valuetype(), "must be a value type");
       push(outer()->mark_as_never_null(klass));
     } else {
       push_object(klass);
--- old/test/hotspot/jtreg/compiler/valhalla/valuetypes/TestNullableValueTypes.java	2019-03-14 15:03:03.010349330 +0100
+++ new/test/hotspot/jtreg/compiler/valhalla/valuetypes/TestNullableValueTypes.java	2019-03-14 15:03:02.870348794 +0100
@@ -675,4 +675,25 @@
             // Expected
         }
     }
+
+    @DontInline
+    public void test25_callee(MyValue1 val) { }
+
+    // Test that when checkcasting from .box to .val and back to .box we
+    // keep track of the information that the value can never be null.
+    @Test(failOn = ALLOC + STORE)
+    public int test25(boolean b, MyValue1.box vt1, MyValue1.val vt2) {
+        vt1 = (MyValue1.val)vt1;
+        Object obj = b ? vt1 : vt2; // We should not allocate here
+        test25_callee(vt1);
+        return ((MyValue1)obj).x;
+    }
+
+    @DontCompile
+    public void test25_verifier(boolean warmup) {
+        int res = test25(true, testValue1, testValue1);
+        Asserts.assertEquals(res, testValue1.x);
+        res = test25(false, testValue1, testValue1);
+        Asserts.assertEquals(res, testValue1.x);
+    }
 }