diff --git a/clang/include/clang/Index/IndexingAction.h b/clang/include/clang/Index/IndexingAction.h
index 36b3c75a65ff2..8b3d5415c063e 100644
--- a/clang/include/clang/Index/IndexingAction.h
+++ b/clang/include/clang/Index/IndexingAction.h
@@ -44,6 +44,8 @@ struct IndexingOptions {
   // 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).
diff --git a/clang/lib/Index/IndexDecl.cpp b/clang/lib/Index/IndexDecl.cpp
index aa73d937df315..eb0b3d4a70e35 100644
--- a/clang/lib/Index/IndexDecl.cpp
+++ b/clang/lib/Index/IndexDecl.cpp
@@ -88,12 +88,11 @@ class IndexingDeclVisitor : public ConstDeclVisitor<IndexingDeclVisitor, bool> {
                                  /*isBase=*/false, isIBType);
     IndexCtx.indexNestedNameSpecifierLoc(D->getQualifierLoc(), Parent);
     if (IndexCtx.shouldIndexFunctionLocalSymbols()) {
-      // Only index parameters in definitions, parameters in declarations are
-      // not useful.
       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 +101,8 @@ class IndexingDeclVisitor : public ConstDeclVisitor<IndexingDeclVisitor, bool> {
           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);
           }
diff --git a/clang/lib/Index/IndexingContext.cpp b/clang/lib/Index/IndexingContext.cpp
index 0bbd739d741c7..3d2d7d4ff02ae 100644
--- a/clang/lib/Index/IndexingContext.cpp
+++ b/clang/lib/Index/IndexingContext.cpp
@@ -40,6 +40,10 @@ bool IndexingContext::shouldIndexImplicitInstantiation() const {
   return IndexOpts.IndexImplicitInstantiation;
 }
 
+bool IndexingContext::shouldIndexParametersInDeclarations() const {
+  return IndexOpts.IndexParametersInDeclarations;
+}
+
 bool IndexingContext::handleDecl(const Decl *D,
                                  SymbolRoleSet Roles,
                                  ArrayRef<SymbolRelation> Relations) {
diff --git a/clang/lib/Index/IndexingContext.h b/clang/lib/Index/IndexingContext.h
index 1de38513c61ab..7765fa73f82c8 100644
--- a/clang/lib/Index/IndexingContext.h
+++ b/clang/lib/Index/IndexingContext.h
@@ -61,6 +61,8 @@ class IndexingContext {
 
   bool shouldIndexImplicitInstantiation() const;
 
+  bool shouldIndexParametersInDeclarations() const;
+
   static bool isTemplateImplicitInstantiation(const Decl *D);
 
   bool handleDecl(const Decl *D, SymbolRoleSet Roles = SymbolRoleSet(),
diff --git a/clang/unittests/Index/IndexTests.cpp b/clang/unittests/Index/IndexTests.cpp
index 147f7a714ad24..2b574a53fc323 100644
--- a/clang/unittests/Index/IndexTests.cpp
+++ b/clang/unittests/Index/IndexTests.cpp
@@ -119,6 +119,21 @@ TEST(IndexTest, IndexPreprocessorMacros) {
   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