diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index d272bfa..17b5ad5 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -2489,6 +2489,10 @@
     if (use.GetUser()->GetBlock() != block) {
       return false;
     }
+    // The append pattern uses the StringBuilder only as the first argument.
+    if (use.GetIndex() != 0u) {
+      return false;
+    }
   }
 
   // Collect args and check for unexpected uses.
@@ -2500,17 +2504,15 @@
   uint32_t format = 0u;
   uint32_t num_args = 0u;
   HInstruction* args[StringBuilderAppend::kMaxArgs];  // Added in reverse order.
-  for (const HUseListNode<HInstruction*>& use : sb->GetUses()) {
-    // The append pattern uses the StringBuilder only as the first argument.
-    if (use.GetIndex() != 0u) {
-      return false;
+  for (HBackwardInstructionIterator iter(block->GetInstructions()); !iter.Done(); iter.Advance()) {
+    HInstruction* user = iter.Current();
+    // Instructions of interest apply to `sb`, skip those that do not involve `sb`.
+    if (user->InputCount() == 0u || user->InputAt(0u) != sb) {
+      continue;
     }
-    // We see the uses in reverse order because they are inserted at the front
-    // of the singly-linked list, so the StringBuilder.append() must come first.
-    HInstruction* user = use.GetUser();
+    // We visit the uses in reverse order, so the StringBuilder.toString() must come first.
     if (!seen_to_string) {
-      if (user->IsInvokeVirtual() &&
-          user->AsInvokeVirtual()->GetIntrinsic() == Intrinsics::kStringBuilderToString) {
+      if (user == invoke) {
         seen_to_string = true;
         continue;
       } else {