Index: clang/lib/AST/Interp/ByteCodeExprGen.h
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.h
+++ clang/lib/AST/Interp/ByteCodeExprGen.h
@@ -263,6 +263,8 @@
   }
 
   bool emitRecordDestruction(const Descriptor *Desc);
+  bool emitDerivedToBaseCasts(const RecordType *DerivedType,
+                              const RecordType *BaseType, const Expr *E);
 
 protected:
   /// Variable to storage mapping.
Index: clang/lib/AST/Interp/ByteCodeExprGen.cpp
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -88,15 +88,8 @@
     if (!this->visit(SubExpr))
       return false;
 
-    const CXXRecordDecl *FromDecl = getRecordDecl(SubExpr);
-    assert(FromDecl);
-    const CXXRecordDecl *ToDecl = getRecordDecl(CE);
-    assert(ToDecl);
-    const Record *R = getRecord(FromDecl);
-    const Record::Base *ToBase = R->getBase(ToDecl);
-    assert(ToBase);
-
-    return this->emitGetPtrBasePop(ToBase->Offset, CE);
+    return this->emitDerivedToBaseCasts(getRecordTy(SubExpr->getType()),
+                                        getRecordTy(CE->getType()), CE);
   }
 
   case CK_FloatingCast: {
@@ -1949,6 +1942,38 @@
     C->emitDestruction();
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::emitDerivedToBaseCasts(
+    const RecordType *DerivedType, const RecordType *BaseType, const Expr *E) {
+  // Pointer of derived type is already on the stack.
+  const CXXRecordDecl *FinalDecl = cast<CXXRecordDecl>(BaseType->getDecl());
+  const RecordDecl *CurDecl = DerivedType->getDecl();
+  const Record *CurRecord = getRecord(CurDecl);
+  assert(CurDecl && FinalDecl);
+  for (;;) {
+    assert(CurRecord->getNumBases() > 0);
+    // One level up
+    for (const Record::Base &B : CurRecord->bases()) {
+      const CXXRecordDecl *BaseDecl = cast<CXXRecordDecl>(B.Decl);
+
+      if (BaseDecl == FinalDecl || BaseDecl->isDerivedFrom(FinalDecl)) {
+        // This decl will lead us to the final decl, so emit a base cast.
+        if (!this->emitGetPtrBasePop(B.Offset, E))
+          return false;
+
+        CurRecord = B.R;
+        CurDecl = BaseDecl;
+        break;
+      }
+    }
+    if (CurDecl == FinalDecl)
+      return true;
+  }
+
+  llvm_unreachable("Couldn't find the base class?");
+  return false;
+}
+
 /// When calling this, we have a pointer of the local-to-destroy
 /// on the stack.
 /// Emit destruction of record types (or arrays of record types).
Index: clang/test/AST/Interp/records.cpp
===================================================================
--- clang/test/AST/Interp/records.cpp
+++ clang/test/AST/Interp/records.cpp
@@ -258,6 +258,10 @@
   class _B : public _A {};
   class _C : public _B {};
   constexpr _C c{12};
+
+  // Cast from A to C.
+  constexpr _A a = c;
+  static_assert(a.a == 12);
 };
 #endif