diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index c118f3818467d9..154acdfbe03276 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2665,7 +2665,8 @@ void ASTDeclReader::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
 
   D->setDeclaredWithTypename(Record.readInt());
 
-  if (D->hasTypeConstraint()) {
+  const bool TypeConstraintInitialized = Record.readBool();
+  if (TypeConstraintInitialized && D->hasTypeConstraint()) {
     ConceptReference *CR = nullptr;
     if (Record.readBool())
       CR = Record.readConceptReference();
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 8a4ca54349e38f..ff1334340874b2 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1880,7 +1880,7 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   Record.push_back(D->wasDeclaredWithTypename());
 
   const TypeConstraint *TC = D->getTypeConstraint();
-  assert((bool)TC == D->hasTypeConstraint());
+  Record.push_back(/*TypeConstraintInitialized=*/TC != nullptr);
   if (TC) {
     auto *CR = TC->getConceptReference();
     Record.push_back(CR != nullptr);
@@ -1898,7 +1898,7 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   if (OwnsDefaultArg)
     Record.AddTemplateArgumentLoc(D->getDefaultArgument());
 
-  if (!TC && !OwnsDefaultArg &&
+  if (!D->hasTypeConstraint() && !OwnsDefaultArg &&
       D->getDeclContext() == D->getLexicalDeclContext() &&
       !D->isInvalidDecl() && !D->hasAttrs() &&
       !D->isTopLevelDeclInObjCContainer() && !D->isImplicit() &&
@@ -2561,6 +2561,7 @@ void ASTWriter::WriteDeclAbbrevs() {
   // TemplateTypeParmDecl
   Abv->Add(
       BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // wasDeclaredWithTypename
+  Abv->Add(BitCodeAbbrevOp(0));                    // TypeConstraintInitialized
   Abv->Add(BitCodeAbbrevOp(0));                    // OwnsDefaultArg
   DeclTemplateTypeParmAbbrev = Stream.EmitAbbrev(std::move(Abv));
 
diff --git a/clang/test/PCH/cxx2a-constraints-crash.cpp b/clang/test/PCH/cxx2a-constraints-crash.cpp
index 637c55f0c879c9..6126a0509fa4a9 100644
--- a/clang/test/PCH/cxx2a-constraints-crash.cpp
+++ b/clang/test/PCH/cxx2a-constraints-crash.cpp
@@ -1,7 +1,5 @@
-// RUN: %clang_cc1 -std=c++2a -emit-pch %s -o %t
-// RUN: %clang_cc1 -std=c++2a -include-pch %t -verify %s
-
-// expected-no-diagnostics
+// RUN: %clang_cc1 -std=c++2a -fallow-pch-with-compiler-errors -emit-pch -o %t %s -verify
+// RUN: %clang_cc1 -std=c++2a -fallow-pch-with-compiler-errors -include-pch %t %s -verify
 
 #ifndef HEADER
 #define HEADER
@@ -27,3 +25,12 @@ int main() {
 }
 
 #endif
+
+namespace GH99036 {
+
+template <typename T>
+concept C; // expected-error {{expected '='}}
+
+template <C U> void f(); // expected-error {{unknown type name 'C'}}
+
+} // namespace GH99036