diff --git a/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp b/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp
--- a/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SymbolCollectorTests.cpp
@@ -1801,6 +1801,23 @@
   EXPECT_THAT(TU.headerSymbols(), Not(Contains(QName("X"))));
 }
 
+TEST_F(SymbolCollectorTest, NoCrashOnObjCMethodCStyleParam) {
+  auto TU = TestTU::withCode(R"objc(
+    /*error-ok*/
+    @interface Foo
+    - (void)fun:(bool)foo
+      bar:(bool)bar,
+      baz:(bool)baz;
+    @end
+  )objc");
+  TU.ExtraArgs.push_back("-xobjective-c++");
+
+  TU.build();
+  // We mostly care about not crashing, but verify that we didn't insert garbage
+  // about X too.
+  EXPECT_THAT(TU.headerSymbols(), Not(Contains(QName("X"))));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -3493,6 +3493,14 @@
       return Result.TakeString();
     }
 
+    if (Method->param_size() > Sel.getNumArgs()) {
+      // FIXME: We could be smarter about this, but for now just avoid a crash
+      // below by returning early.
+      Result.AddTypedTextChunk(
+          Result.getAllocator().CopyString(ND->getNameAsString()));
+      return Result.TakeString();
+    }
+
     std::string SelName = Sel.getNameForSlot(0).str();
     SelName += ':';
     if (StartParameter == 0)