diff --git a/include/swift/IRGen/Linking.h b/include/swift/IRGen/Linking.h
index c8d06aa301bca..e9673973b5163 100644
--- a/include/swift/IRGen/Linking.h
+++ b/include/swift/IRGen/Linking.h
@@ -132,7 +132,7 @@ class LinkEntity {
   /// ValueDecl*, SILFunction*, or TypeBase*, depending on Kind.
   void *Pointer;
 
-  /// ProtocolConformance*, depending on Kind.
+  /// ProtocolConformance* or SILDifferentiabilityWitness*, depending on Kind.
   void *SecondaryPointer;
 
   /// A hand-rolled bitfield with the following layout:
@@ -772,8 +772,8 @@ class LinkEntity {
   void
   setForDifferentiabilityWitness(Kind kind,
                                  const SILDifferentiabilityWitness *witness) {
-    Pointer = const_cast<void *>(static_cast<const void *>(witness));
-    SecondaryPointer = nullptr;
+    Pointer = nullptr;
+    SecondaryPointer = const_cast<void *>(static_cast<const void *>(witness));
     Data = LINKENTITY_SET_FIELD(Kind, unsigned(kind));
   }
 
@@ -1684,7 +1684,7 @@ class LinkEntity {
 
   SILDifferentiabilityWitness *getSILDifferentiabilityWitness() const {
     assert(getKind() == Kind::DifferentiabilityWitness);
-    return reinterpret_cast<SILDifferentiabilityWitness *>(Pointer);
+    return reinterpret_cast<SILDifferentiabilityWitness *>(SecondaryPointer);
   }
 
   const RootProtocolConformance *getRootProtocolConformance() const {
diff --git a/lib/IRGen/IRGenModule.cpp b/lib/IRGen/IRGenModule.cpp
index a3a4ba6857b68..fc5a09cb06a00 100644
--- a/lib/IRGen/IRGenModule.cpp
+++ b/lib/IRGen/IRGenModule.cpp
@@ -1445,7 +1445,7 @@ bool IRGenModule::IsWellKnownBuiltinOrStructralType(CanType T) const {
       T == Context.getAnyObjectType())
     return true;
 
-  if (auto IntTy = dyn_cast<BuiltinIntegerType>(T)) {
+  if (auto IntTy = dyn_cast_or_null<BuiltinIntegerType>(T)) {
     auto Width = IntTy->getWidth();
     if (Width.isPointerWidth())
       return true;