diff --git a/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp b/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
--- a/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
@@ -672,6 +672,24 @@
               ElementsAre(AllOf(Diag(Test.range(), "'main' must return 'int'"),
                                 Not(WithFix(_)))));
 }
+TEST(DiagnosticsTest, Consteval) {
+  Annotations Header(R"cpp(
+    struct Container {
+      consteval Container() {
+        Push();
+      }
+      consteval void Push() {}
+    };
+  )cpp");
+  Annotations Main(R"cpp(
+    #include "a.h"
+    constexpr Container c = Container();
+  )cpp");
+  TestTU TU = TestTU::withCode(Main.code());
+  TU.ExtraArgs.push_back("-std=c++20");
+  TU.AdditionalFiles = {{"a.h", std::string(Header.code())}};
+  EXPECT_THAT(*TU.build().getDiagnostics(), IsEmpty());
+}
 
 TEST(ClangdTest, MSAsm) {
   // Parsing MS assembly tries to use the target MCAsmInfo, which we don't link.
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -2260,7 +2260,7 @@
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Defaulted
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // ExplicitlyDefaulted
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // ImplicitReturnZero
-  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Constexpr
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 2)); // Constexpr
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // UsesSEHTry
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // SkippedBody
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // MultiVersion