Index: include/clang/Index/IndexingAction.h
===================================================================
--- include/clang/Index/IndexingAction.h
+++ include/clang/Index/IndexingAction.h
@@ -44,6 +44,8 @@
   // callback is not available (e.g. after parsing has finished). Note that
   // macro references are not available in Proprocessor.
   bool IndexMacrosInPreprocessor = false;
+  // Has no effect if IndexFunctionLocals are false.
+  bool IndexParametersInDeclarations = false;
 };
 
 /// Creates a frontend action that indexes all symbols (macros and AST decls).
Index: lib/Index/IndexDecl.cpp
===================================================================
--- lib/Index/IndexDecl.cpp
+++ lib/Index/IndexDecl.cpp
@@ -93,7 +93,8 @@
       if (const ParmVarDecl *Parm = dyn_cast<ParmVarDecl>(D)) {
         auto *DC = Parm->getDeclContext();
         if (auto *FD = dyn_cast<FunctionDecl>(DC)) {
-          if (FD->isThisDeclarationADefinition())
+          if (IndexCtx.shouldIndexParametersInDeclarations() ||
+              FD->isThisDeclarationADefinition())
             IndexCtx.handleDecl(Parm);
         } else if (auto *MD = dyn_cast<ObjCMethodDecl>(DC)) {
           if (MD->isThisDeclarationADefinition())
@@ -102,7 +103,8 @@
           IndexCtx.handleDecl(Parm);
         }
       } else if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
-        if (FD->isThisDeclarationADefinition()) {
+        if (IndexCtx.shouldIndexParametersInDeclarations() ||
+            FD->isThisDeclarationADefinition()) {
           for (auto PI : FD->parameters()) {
             IndexCtx.handleDecl(PI);
           }
Index: lib/Index/IndexingContext.h
===================================================================
--- lib/Index/IndexingContext.h
+++ lib/Index/IndexingContext.h
@@ -61,6 +61,8 @@
 
   bool shouldIndexImplicitInstantiation() const;
 
+  bool shouldIndexParametersInDeclarations() const;
+
   static bool isTemplateImplicitInstantiation(const Decl *D);
 
   bool handleDecl(const Decl *D, SymbolRoleSet Roles = SymbolRoleSet(),
Index: lib/Index/IndexingContext.cpp
===================================================================
--- lib/Index/IndexingContext.cpp
+++ lib/Index/IndexingContext.cpp
@@ -40,6 +40,10 @@
   return IndexOpts.IndexImplicitInstantiation;
 }
 
+bool IndexingContext::shouldIndexParametersInDeclarations() const {
+  return IndexOpts.IndexParametersInDeclarations;
+}
+
 bool IndexingContext::handleDecl(const Decl *D,
                                  SymbolRoleSet Roles,
                                  ArrayRef<SymbolRelation> Relations) {
Index: unittests/Index/IndexTests.cpp
===================================================================
--- unittests/Index/IndexTests.cpp
+++ unittests/Index/IndexTests.cpp
@@ -119,6 +119,21 @@
   EXPECT_THAT(Index->Symbols, UnorderedElementsAre());
 }
 
+TEST(IndexTest, IndexParametersInDecls) {
+  std::string Code = "void foo(int bar);";
+  auto Index = std::make_shared<Indexer>();
+  IndexingOptions Opts;
+  Opts.IndexFunctionLocals = true;
+  Opts.IndexParametersInDeclarations = true;
+  tooling::runToolOnCode(new IndexAction(Index, Opts), Code);
+  EXPECT_THAT(Index->Symbols, Contains(QName("bar")));
+
+  Opts.IndexParametersInDeclarations = false;
+  Index->Symbols.clear();
+  tooling::runToolOnCode(new IndexAction(Index, Opts), Code);
+  EXPECT_THAT(Index->Symbols, Not(Contains(QName("bar"))));
+}
+
 } // namespace
 } // namespace index
 } // namespace clang