diff --git a/clang-tools-extra/clangd/CollectMacros.h b/clang-tools-extra/clangd/CollectMacros.h
--- a/clang-tools-extra/clangd/CollectMacros.h
+++ b/clang-tools-extra/clangd/CollectMacros.h
@@ -12,6 +12,7 @@
 #include "Protocol.h"
 #include "SourceCode.h"
 #include "index/SymbolID.h"
+#include "clang/Basic/SourceLocation.h"
 #include "clang/Lex/PPCallbacks.h"
 #include "clang/Lex/Preprocessor.h"
 #include "llvm/ADT/DenseMap.h"
@@ -61,11 +62,16 @@
                       const clang::MacroDefinition &MD,
                       const clang::MacroDirective *Undef) override;
 
-  // FIXME: handle C++23 #elifdef, #elifndef
   void Ifdef(SourceLocation Loc, const Token &MacroName,
              const MacroDefinition &MD) override;
   void Ifndef(SourceLocation Loc, const Token &MacroName,
               const MacroDefinition &MD) override;
+  using PPCallbacks::Elifdef;
+  using PPCallbacks::Elifndef;
+  void Elifdef(SourceLocation Loc, const Token &MacroNameTok,
+               const MacroDefinition &MD) override;
+  void Elifndef(SourceLocation Loc, const Token &MacroNameTok,
+                const MacroDefinition &MD) override;
 
   void Defined(const Token &MacroName, const MacroDefinition &MD,
                SourceRange Range) override;
diff --git a/clang-tools-extra/clangd/CollectMacros.cpp b/clang-tools-extra/clangd/CollectMacros.cpp
--- a/clang-tools-extra/clangd/CollectMacros.cpp
+++ b/clang-tools-extra/clangd/CollectMacros.cpp
@@ -36,33 +36,51 @@
                                         SrcMgr::CharacteristicKind, FileID) {
   InMainFile = isInsideMainFile(Loc, SM);
 }
+
 void CollectMainFileMacros::MacroExpands(const Token &MacroName,
                                          const MacroDefinition &MD,
                                          SourceRange Range,
                                          const MacroArgs *Args) {
   add(MacroName, MD.getMacroInfo());
 }
+
 void CollectMainFileMacros::MacroUndefined(const clang::Token &MacroName,
                                            const clang::MacroDefinition &MD,
                                            const clang::MacroDirective *Undef) {
   add(MacroName, MD.getMacroInfo());
 }
+
 void CollectMainFileMacros::Ifdef(SourceLocation Loc, const Token &MacroName,
                                   const MacroDefinition &MD) {
   add(MacroName, MD.getMacroInfo(), /*IsDefinition=*/false,
       /*InConditionalDirective=*/true);
 }
+
 void CollectMainFileMacros::Ifndef(SourceLocation Loc, const Token &MacroName,
                                    const MacroDefinition &MD) {
   add(MacroName, MD.getMacroInfo(), /*IsDefinition=*/false,
       /*InConditionalDirective=*/true);
 }
+
+void CollectMainFileMacros::Elifdef(SourceLocation Loc, const Token &MacroName,
+                                    const MacroDefinition &MD) {
+  add(MacroName, MD.getMacroInfo(), /*IsDefinition=*/false,
+      /*InConditionalDirective=*/true);
+}
+
+void CollectMainFileMacros::Elifndef(SourceLocation Loc, const Token &MacroName,
+                                     const MacroDefinition &MD) {
+  add(MacroName, MD.getMacroInfo(), /*IsDefinition=*/false,
+      /*InConditionalDirective=*/true);
+}
+
 void CollectMainFileMacros::Defined(const Token &MacroName,
                                     const MacroDefinition &MD,
                                     SourceRange Range) {
   add(MacroName, MD.getMacroInfo(), /*IsDefinition=*/false,
       /*InConditionalDirective=*/true);
 }
+
 void CollectMainFileMacros::SourceRangeSkipped(SourceRange R,
                                                SourceLocation EndifLoc) {
   if (!InMainFile)
diff --git a/clang-tools-extra/clangd/unittests/CollectMacrosTests.cpp b/clang-tools-extra/clangd/unittests/CollectMacrosTests.cpp
--- a/clang-tools-extra/clangd/unittests/CollectMacrosTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CollectMacrosTests.cpp
@@ -56,6 +56,11 @@
       // )cpp",
       R"cpp(
         #ifdef $Unknown(condit)[[UNDEFINED]]
+        #elifdef $Unknown(condit)[[UNDEFINED]]
+        #endif
+
+        #ifdef $Unknown(condit)[[UNDEFINED]]
+        #elifndef $Unknown(condit)[[UNDEFINED]]
         #endif
 
         #ifndef $Unknown(condit)[[UNDEFINED]]
@@ -101,11 +106,12 @@
 
   for (const char *Test : Tests) {
     Annotations T(Test);
-    auto AST = TestTU::withCode(T.code()).build();
+    auto Inputs = TestTU::withCode(T.code());
+    Inputs.ExtraArgs.push_back("-std=c++2b");
+    auto AST = Inputs.build();
     auto ActualMacroRefs = AST.getMacros();
     auto &SM = AST.getSourceManager();
     auto &PP = AST.getPreprocessor();
-
     for (const auto &[Name, Ranges] : T.all_ranges()) {
       if (Name == "Unknown") {
         EXPECT_THAT(ActualMacroRefs.UnknownMacros,