Scope `string` usage with the namespace.
diff --git a/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc b/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
index 3002c8c..599023b 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
@@ -1745,7 +1745,7 @@
TrimWhitespace(&proto_file);
if (!proto_file.empty()) {
std::map<std::string, std::string>::iterator existing_entry =
- map_->find(string(proto_file));
+ map_->find(std::string(proto_file));
if (existing_entry != map_->end()) {
std::cerr << "warning: duplicate proto file reference, replacing "
"framework entry for '"
