diff --git a/clang/lib/Tooling/Syntax/BuildTree.cpp b/clang/lib/Tooling/Syntax/BuildTree.cpp
--- a/clang/lib/Tooling/Syntax/BuildTree.cpp
+++ b/clang/lib/Tooling/Syntax/BuildTree.cpp
@@ -558,7 +558,7 @@
       assert(A.getTokenBuffer().expandedTokens().back().kind() == tok::eof);
       // Create all leaf nodes.
       // Note that we do not have 'eof' in the tree.
-      for (auto &T : A.getTokenBuffer().expandedTokens().drop_back()) {
+      for (const auto &T : A.getTokenBuffer().expandedTokens().drop_back()) {
         auto *L = new (A.getAllocator()) syntax::Leaf(&T);
         L->Original = true;
         L->CanModify = A.getTokenBuffer().spelledForExpanded(T).hasValue();
diff --git a/clang/lib/Tooling/Syntax/ComputeReplacements.cpp b/clang/lib/Tooling/Syntax/ComputeReplacements.cpp
--- a/clang/lib/Tooling/Syntax/ComputeReplacements.cpp
+++ b/clang/lib/Tooling/Syntax/ComputeReplacements.cpp
@@ -32,7 +32,7 @@
   private:
     void process(const syntax::Node *N) {
       if (auto *T = dyn_cast<syntax::Tree>(N)) {
-        for (auto *C = T->getFirstChild(); C != nullptr;
+        for (const auto *C = T->getFirstChild(); C != nullptr;
              C = C->getNextSibling())
           process(C);
         return;
@@ -64,8 +64,8 @@
 
 syntax::FileRange rangeOfExpanded(const syntax::Arena &A,
                                   llvm::ArrayRef<syntax::Token> Expanded) {
-  auto &Buffer = A.getTokenBuffer();
-  auto &SM = A.getSourceManager();
+  const auto &Buffer = A.getTokenBuffer();
+  const auto &SM = A.getSourceManager();
 
   // Check that \p Expanded actually points into expanded tokens.
   assert(Buffer.expandedTokens().begin() <= Expanded.begin());
@@ -85,8 +85,8 @@
 tooling::Replacements
 syntax::computeReplacements(const syntax::Arena &A,
                             const syntax::TranslationUnit &TU) {
-  auto &Buffer = A.getTokenBuffer();
-  auto &SM = A.getSourceManager();
+  const auto &Buffer = A.getTokenBuffer();
+  const auto &SM = A.getSourceManager();
 
   tooling::Replacements Replacements;
   // Text inserted by the replacement we are building now.
diff --git a/clang/lib/Tooling/Syntax/Tree.cpp b/clang/lib/Tooling/Syntax/Tree.cpp
--- a/clang/lib/Tooling/Syntax/Tree.cpp
+++ b/clang/lib/Tooling/Syntax/Tree.cpp
@@ -19,7 +19,7 @@
 static void traverse(const syntax::Node *N,
                      llvm::function_ref<void(const syntax::Node *)> Visit) {
   if (auto *T = dyn_cast<syntax::Tree>(N)) {
-    for (auto *C = T->getFirstChild(); C; C = C->getNextSibling())
+    for (const auto *C = T->getFirstChild(); C; C = C->getNextSibling())
       traverse(C, Visit);
   }
   Visit(N);
@@ -226,7 +226,7 @@
   auto *T = dyn_cast<Tree>(this);
   if (!T)
     return;
-  for (auto *C = T->getFirstChild(); C; C = C->getNextSibling()) {
+  for (const auto *C = T->getFirstChild(); C; C = C->getNextSibling()) {
     if (T->isOriginal())
       assert(C->isOriginal());
     assert(!C->isDetached());