diff --git a/CMakeLists.txt b/CMakeLists.txt
index a54379c..6ae97bd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,8 +1,14 @@
-cmake_minimum_required(VERSION 3.16)
+cmake_minimum_required(VERSION 4.0)
 enable_testing()
 
 project(O2CodeChecker)
 
+# LLVM's installed HandleLLVMOptions.cmake sets no C++ standard, so without this
+# we inherit whatever the compiler defaults to -- C++14 on Apple clang, which is
+# not enough for the clang-tidy headers.
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
 # find clang + llvm
 find_package(Clang REQUIRED CONFIG)
 
diff --git a/aliceO2/AliceO2TidyModule.cpp b/aliceO2/AliceO2TidyModule.cpp
index 71f5ac1..4c6f73d 100644
--- a/aliceO2/AliceO2TidyModule.cpp
+++ b/aliceO2/AliceO2TidyModule.cpp
@@ -9,7 +9,14 @@
 
 #include "clang-tidy/ClangTidy.h"
 #include "clang-tidy/ClangTidyModule.h"
+// Up to Clang 21 ClangTidyModuleRegistry was declared only in
+// ClangTidyModuleRegistry.h. Clang 22 moved it into ClangTidyModule.h above and
+// left the old header behind as a bare #warning, to be deleted in Clang 24 --
+// so __has_include() would keep including it, and keep warning, on 22 and 23.
+#include "llvm/Config/llvm-config.h"
+#if LLVM_VERSION_MAJOR < 22
 #include "clang-tidy/ClangTidyModuleRegistry.h"
+#endif
 #include "MemberNamesCheck.h"
 #include "NamespaceNamingCheck.h"
 #include "SizeofCheck.h"
diff --git a/aliceO2/NamespaceNamingCheck.cpp b/aliceO2/NamespaceNamingCheck.cpp
index ca9790a..000399b 100644
--- a/aliceO2/NamespaceNamingCheck.cpp
+++ b/aliceO2/NamespaceNamingCheck.cpp
@@ -11,6 +11,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchersMacros.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "llvm/Config/llvm-config.h"   // LLVM_VERSION_MAJOR
 #include <regex>
 #include <string>
 #include <ctype.h>
@@ -98,7 +99,23 @@ void NamespaceNamingCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *MatchedNamespaceLoc = Result.Nodes.getNodeAs<NestedNameSpecifierLoc>("namespace-usage");
   if( MatchedNamespaceLoc )
   {
-    const auto *AsNamespace = MatchedNamespaceLoc->getNestedNameSpecifier()->getAsNamespace();
+#if LLVM_VERSION_MAJOR >= 22
+    // Clang 22 turned NestedNameSpecifier into a value type and removed
+    // getAsNamespace(); the namespace is now reached through
+    // getAsNamespaceAndPrefix(), which is llvm_unreachable() unless the
+    // specifier really designates one. The matcher below only binds
+    // specifiesNamespace(), but check the kind rather than trust that. It also
+    // yields a NamespaceBaseDecl, the new common base of NamespaceDecl and
+    // NamespaceAliasDecl; both are NamedDecl, which is all we use below.
+    const NestedNameSpecifier Qualifier = MatchedNamespaceLoc->getNestedNameSpecifier();
+    if( Qualifier.getKind() != NestedNameSpecifier::Kind::Namespace )
+    {
+      return;
+    }
+    const NamespaceBaseDecl *AsNamespace = Qualifier.getAsNamespaceAndPrefix().Namespace;
+#else
+    const NamespaceDecl *AsNamespace = MatchedNamespaceLoc->getNestedNameSpecifier()->getAsNamespace();
+#endif
     if( isOutsideOfTargetScope( Result.SourceManager->getFilename(AsNamespace->getLocation()).str() ) )
     {
       return;