diff --git a/docs/ReleaseNotes.md b/docs/ReleaseNotes.md
index 375d68d2fa..f7291b1987 100644
--- a/docs/ReleaseNotes.md
+++ b/docs/ReleaseNotes.md
@@ -63,6 +63,9 @@ line upon naming the release. Refer to previous for appropriate section names.
 - The `shared` and `uniform` keywords are removed in HLSL 202x, with
   compatibility warnings available for earlier language versions
   [#8482](https://github.com/microsoft/DirectXShaderCompiler/issues/8482).
+- HLSL 202x disallows putting cbuffer, tbuffer, or namespace declarations inside
+  a cbuffer or tbuffer
+  [#8484](https://github.com/microsoft/DirectXShaderCompiler/issues/8484).
 
 #### SPIR-V
 
diff --git a/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td b/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td
index cc7a4662f1..650bce5874 100644
--- a/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/tools/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7926,6 +7926,8 @@ def err_hlsl_unsupported_object_context
     "entry function parameters|entry function return type|"
     "patch constant function parameters|patch constant function return type|"
     "payload parameters|attributes|builtin template parameters|structured buffers|global variables|groupshared variables}1">;
+def err_hlsl_unsupported_declaration_in_buffer : Error<
+  "unsupported declaration %0 in %select{tbuffer|cbuffer}1 declaration">;
 def err_hlsl_logical_binop_scalar : Error<
    "operands for short-circuiting logical binary operator must be scalar, for non-scalar types use '%select{and|or}0'">;
 def err_hlsl_ternary_scalar : Error<
diff --git a/tools/clang/lib/Sema/SemaHLSL.cpp b/tools/clang/lib/Sema/SemaHLSL.cpp
index 274adae6d7..4808ecd328 100644
--- a/tools/clang/lib/Sema/SemaHLSL.cpp
+++ b/tools/clang/lib/Sema/SemaHLSL.cpp
@@ -15363,6 +15363,19 @@ void Sema::ActOnFinishHLSLBuffer(Decl *Dcl, SourceLocation RBrace) {
   bool HasPackOffset = false;
   bool HasNonPackOffset = false;
   for (auto *Field : BufDecl->decls()) {
+    // HLSL 202x 0005 Cbuffer Contexts proposal restricts the contents of a
+    // cbuffer to classes (records), functions, variables, and empty
+    // declarations (see: https://hlsl-tc57.github.io/tc57/proposal/0005/)
+    if (getLangOpts().HLSLVersion >= hlsl::LangStd::v202x &&
+        (isa<HLSLBufferDecl>(Field) || isa<NamespaceDecl>(Field))) {
+      NamedDecl *ND = cast<NamedDecl>(Field);
+      Diag(Field->getLocation(),
+           diag::err_hlsl_unsupported_declaration_in_buffer)
+          << ND << BufDecl->isCBuffer();
+      Diag(Dcl->getLocation(), diag::note_declared_at);
+      Dcl->setInvalidDecl();
+    }
+
     VarDecl *Var = dyn_cast<VarDecl>(Field);
     if (!Var)
       continue;
diff --git a/tools/clang/test/SemaHLSL/hlsl/202x-cbuffer-contexts.hlsl b/tools/clang/test/SemaHLSL/hlsl/202x-cbuffer-contexts.hlsl
new file mode 100644
index 0000000000..212e505152
--- /dev/null
+++ b/tools/clang/test/SemaHLSL/hlsl/202x-cbuffer-contexts.hlsl
@@ -0,0 +1,57 @@
+// RUN: %dxc -T lib_6_9 -verify -HV 202x %s
+
+cbuffer A { // expected-note{{declared here}}
+  int Y;
+  // expected-error@+1 {{unsupported declaration 'N' in cbuffer declaration}}
+  namespace N {
+  }
+  float4 F5;
+}
+
+cbuffer A { // expected-note{{declared here}}
+  // expected-error@+1 {{unsupported declaration 'Nested' in cbuffer declaration}}
+  cbuffer Nested {
+  }
+}
+
+tbuffer TB { // expected-note{{declared here}}
+  // expected-error@+1 {{unsupported declaration 'NS' in tbuffer declaration}}
+  namespace NS {}
+}
+
+tbuffer TB2 { // expected-note{{declared here}}
+  // expected-error@+1{{unsupported declaration 'CB2' in tbuffer declaration}}
+  cbuffer CB2 {
+    int X;
+  }
+}
+
+namespace Valid {
+  cbuffer CBValid {
+    int CompletelyFine;
+  }
+
+  tbuffer TBValid {
+    float StillFine;
+  }
+
+  cbuffer GoingOffTheRails { // expected-note{{declared here}}
+    // expected-error@+1{{unsupported declaration 'NotCool' in cbuffer declaration}}
+    tbuffer NotCool {
+      ; // even if it is empty...
+    }
+  }
+
+  cbuffer GoingOffTheRailsAgain { // expected-note{{declared here}}
+    // expected-error@+1{{unsupported declaration 'StillNotCool' in cbuffer declaration}}
+    tbuffer StillNotCool { // expected-note{{declared here}}
+      // expected-error@+1{{unsupported declaration 'Turtles' in tbuffer declaration}}
+      cbuffer Turtles { // expected-note{{declared here}}
+        // expected-error@+1{{unsupported declaration 'AllTheWayDown' in cbuffer declaration}}
+        tbuffer AllTheWayDown {
+          ;
+        }
+      }
+    }
+  }
+}