diff --git a/llvm/lib/VMCore/Type.cpp b/llvm/lib/VMCore/Type.cpp
index f4fad667a13c..d19dc06caa16 100644
--- a/llvm/lib/VMCore/Type.cpp
+++ b/llvm/lib/VMCore/Type.cpp
@@ -707,7 +707,12 @@ PointerType *PointerType::get(Type *EltTy, unsigned AddressSpace) {
 
 PointerType::PointerType(Type *E, unsigned AddrSpace)
   : SequentialType(PointerTyID, E) {
+#ifndef NDEBUG
+  const unsigned oldNCT = NumContainedTys;
+#endif
   setSubclassData(AddrSpace);
+  // Check for miscompile. PR11652.
+  assert(oldNCT == NumContainedTys && "bitfield written out of bounds?");
 }
 
 PointerType *Type::getPointerTo(unsigned addrs) {