diff --git a/clang-tools-extra/clangd/SemanticHighlighting.h b/clang-tools-extra/clangd/SemanticHighlighting.h
--- a/clang-tools-extra/clangd/SemanticHighlighting.h
+++ b/clang-tools-extra/clangd/SemanticHighlighting.h
@@ -67,6 +67,7 @@
   Static,
   Abstract,
   DependentName,
+  DefaultLibrary,
 
   FunctionScope,
   ClassScope,
diff --git a/clang-tools-extra/clangd/SemanticHighlighting.cpp b/clang-tools-extra/clangd/SemanticHighlighting.cpp
--- a/clang-tools-extra/clangd/SemanticHighlighting.cpp
+++ b/clang-tools-extra/clangd/SemanticHighlighting.cpp
@@ -245,6 +245,16 @@
   return false;
 }
 
+/// Returns true if `Decl` is considered to be from a default/system library.
+/// This currently checks the systemness of the file by include type, although
+/// different heuristics may be used in the future (e.g. sysroot paths).
+bool isDefaultLibrary(const Decl *D) {
+  SourceLocation Loc = D->getLocation();
+  if (!Loc.isValid())
+    return false;
+  return D->getASTContext().getSourceManager().isInSystemHeader(Loc);
+}
+
 // For a macro usage `DUMP(foo)`, we want:
 //  - DUMP --> "macro"
 //  - foo --> "variable".
@@ -420,6 +430,8 @@
 };
 
 llvm::Optional<HighlightingModifier> scopeModifier(const NamedDecl *D) {
+  if (!D)
+    return llvm::None;
   const DeclContext *DC = D->getDeclContext();
   // Injected "Foo" within the class "Foo" has file scope, not class scope.
   if (auto *R = dyn_cast_or_null<RecordDecl>(D))
@@ -456,6 +468,8 @@
     return scopeModifier(TD->getDecl());
   if (auto *TD = T->getAsTagDecl())
     return scopeModifier(TD);
+  if (auto *OT = dyn_cast<ObjCObjectType>(T))
+    return scopeModifier(OT->getInterface());
   return llvm::None;
 }
 
@@ -493,7 +507,7 @@
   // We handle objective-C selectors specially, because one reference can
   // cover several non-contiguous tokens.
   void highlightObjCSelector(const ArrayRef<SourceLocation> &Locs, bool Decl,
-                             bool Class) {
+                             bool Class, bool DefaultLibrary) {
     HighlightingKind Kind =
         Class ? HighlightingKind::StaticMethod : HighlightingKind::Method;
     for (SourceLocation Part : Locs) {
@@ -503,20 +517,27 @@
         Tok.addModifier(HighlightingModifier::Declaration);
       if (Class)
         Tok.addModifier(HighlightingModifier::Static);
+      if (DefaultLibrary)
+        Tok.addModifier(HighlightingModifier::DefaultLibrary);
     }
   }
 
   bool VisitObjCMethodDecl(ObjCMethodDecl *OMD) {
     llvm::SmallVector<SourceLocation> Locs;
     OMD->getSelectorLocs(Locs);
-    highlightObjCSelector(Locs, /*Decl=*/true, OMD->isClassMethod());
+    highlightObjCSelector(Locs, /*Decl=*/true, OMD->isClassMethod(),
+                          isDefaultLibrary(OMD));
     return true;
   }
 
   bool VisitObjCMessageExpr(ObjCMessageExpr *OME) {
     llvm::SmallVector<SourceLocation> Locs;
     OME->getSelectorLocs(Locs);
-    highlightObjCSelector(Locs, /*Decl=*/false, OME->isClassMessage());
+    bool DefaultLibrary = false;
+    if (ObjCMethodDecl *OMD = OME->getMethodDecl())
+      DefaultLibrary = isDefaultLibrary(OMD);
+    highlightObjCSelector(Locs, /*Decl=*/false, OME->isClassMessage(),
+                          DefaultLibrary);
     return true;
   }
 
@@ -642,6 +663,8 @@
             Tok.addModifier(HighlightingModifier::Abstract);
           if (isDependent(Decl))
             Tok.addModifier(HighlightingModifier::DependentName);
+          if (isDefaultLibrary(Decl))
+            Tok.addModifier(HighlightingModifier::DefaultLibrary);
           if (Decl->isDeprecated())
             Tok.addModifier(HighlightingModifier::Deprecated);
           // Do not treat an UnresolvedUsingValueDecl as a declaration.
@@ -826,6 +849,8 @@
     return "abstract";
   case HighlightingModifier::DependentName:
     return "dependentName"; // nonstandard
+  case HighlightingModifier::DefaultLibrary:
+    return "defaultLibrary";
   case HighlightingModifier::FunctionScope:
     return "functionScope"; // nonstandard
   case HighlightingModifier::ClassScope:
diff --git a/clang-tools-extra/clangd/test/initialize-params.test b/clang-tools-extra/clangd/test/initialize-params.test
--- a/clang-tools-extra/clangd/test/initialize-params.test
+++ b/clang-tools-extra/clangd/test/initialize-params.test
@@ -90,6 +90,7 @@
 # CHECK-NEXT:            "static",
 # CHECK-NEXT:            "abstract",
 # CHECK-NEXT:            "dependentName",
+# CHECK-NEXT:            "defaultLibrary",
 # CHECK-NEXT:            "functionScope",
 # CHECK-NEXT:            "classScope",
 # CHECK-NEXT:            "fileScope",
diff --git a/clang-tools-extra/clangd/test/semantic-tokens.test b/clang-tools-extra/clangd/test/semantic-tokens.test
--- a/clang-tools-extra/clangd/test/semantic-tokens.test
+++ b/clang-tools-extra/clangd/test/semantic-tokens.test
@@ -23,7 +23,7 @@
 # CHECK-NEXT:      4,
 # CHECK-NEXT:      1,
 # CHECK-NEXT:      0,
-# CHECK-NEXT:      1025
+# CHECK-NEXT:      2049
 # CHECK-NEXT:    ],
 # CHECK-NEXT:    "resultId": "1"
 # CHECK-NEXT:  }
@@ -49,7 +49,7 @@
 # CHECK-NEXT:          4,
 # CHECK-NEXT:          1,
 # CHECK-NEXT:          0,
-# CHECK-NEXT:          1025
+# CHECK-NEXT:          2049
 # CHECK-NEXT:        ],
 #                    Inserted at position 1
 # CHECK-NEXT:        "deleteCount": 0,
@@ -72,12 +72,12 @@
 # CHECK-NEXT:      4,
 # CHECK-NEXT:      1,
 # CHECK-NEXT:      0,
-# CHECK-NEXT:      1025,
+# CHECK-NEXT:      2049,
 # CHECK-NEXT:      1,
 # CHECK-NEXT:      4,
 # CHECK-NEXT:      1,
 # CHECK-NEXT:      0,
-# CHECK-NEXT:      1025
+# CHECK-NEXT:      2049
 # CHECK-NEXT:    ],
 # CHECK-NEXT:    "resultId": "3"
 # CHECK-NEXT:  }
diff --git a/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp b/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp
--- a/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp
@@ -69,13 +69,16 @@
                         std::vector<std::pair</*FileName*/ llvm::StringRef,
                                               /*FileContent*/ llvm::StringRef>>
                             AdditionalFiles = {},
-                        uint32_t ModifierMask = -1) {
+                        uint32_t ModifierMask = -1,
+                        std::vector<std::string> AdditionalArgs = {}) {
   Annotations Test(Code);
   TestTU TU;
   TU.Code = std::string(Test.code());
 
   TU.ExtraArgs.push_back("-std=c++20");
   TU.ExtraArgs.push_back("-xobjective-c++");
+  TU.ExtraArgs.insert(std::end(TU.ExtraArgs), std::begin(AdditionalArgs),
+                      std::end(AdditionalArgs));
 
   for (auto File : AdditionalFiles)
     TU.AdditionalFiles.insert({File.first, std::string(File.second)});
@@ -731,6 +734,24 @@
     #define DEFINE_Y DEFINE(Y)
   )cpp"}},
                      ~ScopeModifierMask);
+
+  checkHighlightings(R"cpp(
+    #include "SYSObject.h"
+    @interface $Class_defaultLibrary[[SYSObject]] ($Namespace_decl[[UserCategory]])
+    @property(nonatomic, readonly) int $Field_decl_readonly[[user_property]];
+    @end
+    int $Function_decl[[somethingUsingSystemSymbols]]() {
+      $Class_defaultLibrary[[SYSObject]] *$LocalVariable_decl[[obj]] = [$Class_defaultLibrary[[SYSObject]] $StaticMethod_static_defaultLibrary[[new]]];
+      return $LocalVariable[[obj]].$Field_defaultLibrary[[value]] + $LocalVariable[[obj]].$Field_readonly[[user_property]];
+    }
+  )cpp",
+                     {{"SystemSDK/SYSObject.h", R"cpp(
+    @interface SYSObject
+    @property(nonatomic, assign) int value;
+    + (instancetype)new;
+    @end
+  )cpp"}},
+                     ~ScopeModifierMask, {"-isystemSystemSDK/"});
 }
 
 TEST(SemanticHighlighting, ScopeModifiers) {