diff --git a/clang/lib/Sema/HLSLExternalSemaSource.cpp b/clang/lib/Sema/HLSLExternalSemaSource.cpp
index e118dda4780e2..a4bd87c9f9a39 100644
--- a/clang/lib/Sema/HLSLExternalSemaSource.cpp
+++ b/clang/lib/Sema/HLSLExternalSemaSource.cpp
@@ -473,6 +473,8 @@ void HLSLExternalSemaSource::defineHLSLTypesWithForwardDeclarations() {
                     /*RawBuffer=*/true, /*HasCounter=*/false)
         .completeDefinition();
   });
+  CompleteType(Decl);
+
   Decl = BuiltinTypeDeclBuilder(*SemaPtr, HLSLNamespace, "RWByteAddressBuffer")
              .finalizeForwardDeclaration();
   onCompletion(Decl, [this](CXXRecordDecl *Decl) {
@@ -480,6 +482,8 @@ void HLSLExternalSemaSource::defineHLSLTypesWithForwardDeclarations() {
                     /*RawBuffer=*/true, /*HasCounter=*/false)
         .completeDefinition();
   });
+  CompleteType(Decl);
+
   Decl = BuiltinTypeDeclBuilder(*SemaPtr, HLSLNamespace,
                                 "RasterizerOrderedByteAddressBuffer")
              .finalizeForwardDeclaration();
@@ -488,6 +492,17 @@ void HLSLExternalSemaSource::defineHLSLTypesWithForwardDeclarations() {
                     /*RawBuffer=*/true, /*HasCounter=*/false)
         .completeDefinition();
   });
+  CompleteType(Decl);
+
+  Decl = BuiltinTypeDeclBuilder(*SemaPtr, HLSLNamespace, "ConstantBuffer")
+             .addSimpleTemplateParams({"element_type"}, StructuredBufferConcept)
+             .finalizeForwardDeclaration();
+  onCompletion(Decl, [this](CXXRecordDecl *Decl) {
+    setupBufferType(Decl, *SemaPtr, ResourceClass::CBuffer, /*IsROV=*/true,
+                    /*RawBuffer=*/false, /*HasCounter=*/false)
+        .completeDefinition();
+  });
+  CompleteType(Decl);
 }
 
 void HLSLExternalSemaSource::onCompletion(CXXRecordDecl *Record,