diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
index 70ce1c3750bbf..de02418076503 100644
--- a/clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -143,6 +143,7 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
   case CK_NonAtomicToAtomic:
   case CK_NoOp:
   case CK_UserDefinedConversion:
+  case CK_BitCast:
     return this->visit(SubExpr);
 
   case CK_IntegralToBoolean:
diff --git a/clang/lib/AST/Interp/Interp.h b/clang/lib/AST/Interp/Interp.h
index ee3b953bb69cc..9eae79ba5d1e7 100644
--- a/clang/lib/AST/Interp/Interp.h
+++ b/clang/lib/AST/Interp/Interp.h
@@ -701,7 +701,9 @@ inline bool CmpHelper<Pointer>(InterpState &S, CodePtr OpPC, CompareFn Fn) {
 
   if (!Pointer::hasSameBase(LHS, RHS)) {
     const SourceInfo &Loc = S.Current->getSource(OpPC);
-    S.FFDiag(Loc, diag::note_invalid_subexpr_in_const_expr);
+    S.FFDiag(Loc, diag::note_constexpr_pointer_comparison_unspecified)
+        << LHS.toDiagnosticString(S.getCtx())
+        << RHS.toDiagnosticString(S.getCtx());
     return false;
   } else {
     unsigned VL = LHS.getByteOffset();
diff --git a/clang/lib/AST/Interp/Pointer.cpp b/clang/lib/AST/Interp/Pointer.cpp
index 00943dc846d3b..e0ea25d8f560b 100644
--- a/clang/lib/AST/Interp/Pointer.cpp
+++ b/clang/lib/AST/Interp/Pointer.cpp
@@ -145,6 +145,13 @@ APValue Pointer::toAPValue() const {
   return APValue(Base, Offset, Path, IsOnePastEnd, IsNullPtr);
 }
 
+std::string Pointer::toDiagnosticString(const ASTContext &Ctx) const {
+  if (!Pointee)
+    return "nullptr";
+
+  return toAPValue().getAsString(Ctx, getType());
+}
+
 bool Pointer::isInitialized() const {
   assert(Pointee && "Cannot check if null pointer was initialized");
   const Descriptor *Desc = getFieldDesc();
diff --git a/clang/test/AST/Interp/literals.cpp b/clang/test/AST/Interp/literals.cpp
index 10e0330daecbd..d2b5f4a5a1901 100644
--- a/clang/test/AST/Interp/literals.cpp
+++ b/clang/test/AST/Interp/literals.cpp
@@ -122,6 +122,35 @@ namespace PointerToBool {
   static_assert(!!FP, "");
 }
 
+namespace PointerComparison {
+
+  struct S { int a, b; } s;
+  constexpr void *null = 0;
+  constexpr void *pv = (void*)&s.a;
+  constexpr void *qv = (void*)&s.b;
+  constexpr bool v1 = null < (int*)0;
+  constexpr bool v2 = null < pv; // expected-error {{must be initialized by a constant expression}} \
+                                 // expected-note {{comparison between 'nullptr' and '&s.a' has unspecified value}} \
+                                 // ref-error {{must be initialized by a constant expression}} \
+                                 // ref-note {{comparison between 'nullptr' and '&s.a' has unspecified value}} \
+
+  constexpr bool v3 = null == pv; // ok
+  constexpr bool v4 = qv == pv; // ok
+
+  /// FIXME: These two are rejected by the current interpreter, but
+  ///   accepted by GCC.
+  constexpr bool v5 = qv >= pv; // ref-error {{constant expression}} \
+                                // ref-note {{unequal pointers to void}}
+  constexpr bool v8 = qv > (void*)&s.a; // ref-error {{constant expression}} \
+                                        // ref-note {{unequal pointers to void}}
+  constexpr bool v6 = qv > null; // expected-error {{must be initialized by a constant expression}} \
+                                 // expected-note {{comparison between '&s.b' and 'nullptr' has unspecified value}} \
+                                 // ref-error {{must be initialized by a constant expression}} \
+                                 // ref-note {{comparison between '&s.b' and 'nullptr' has unspecified value}}
+
+  constexpr bool v7 = qv <= (void*)&s.b; // ok
+}
+
 namespace SizeOf {
   constexpr int soint = sizeof(int);
   constexpr int souint = sizeof(unsigned int);