diff --git a/python/google/protobuf/pyext/extension_dict.h b/python/google/protobuf/pyext/extension_dict.h
index 0cac8ba6..352495b9 100644
--- a/python/google/protobuf/pyext/extension_dict.h
+++ b/python/google/protobuf/pyext/extension_dict.h
@@ -47,8 +47,9 @@ namespace protobuf {
 class Message;
 class FieldDescriptor;
 
+#ifdef _SHARED_PTR_H
 using std::shared_ptr;
-using std::string;
+#endif
 
 namespace python {
 
diff --git a/python/google/protobuf/pyext/message.h b/python/google/protobuf/pyext/message.h
index d4b7f4cf..5b495e89 100644
--- a/python/google/protobuf/pyext/message.h
+++ b/python/google/protobuf/pyext/message.h
@@ -52,8 +52,10 @@ class Descriptor;
 class DescriptorPool;
 class MessageFactory;
 
+#ifdef _SHARED_PTR_H
 using std::shared_ptr;
 using std::string;
+#endif
 
 namespace python {
 
diff --git a/python/google/protobuf/pyext/message_map_container.h b/python/google/protobuf/pyext/message_map_container.h
index 270922d4..d65ac4dd 100644
--- a/python/google/protobuf/pyext/message_map_container.h
+++ b/python/google/protobuf/pyext/message_map_container.h
@@ -45,8 +45,9 @@ namespace protobuf {
 
 class Message;
 
+#ifdef _SHARED_PTR_H
 using std::shared_ptr;
-using std::string;
+#endif
 
 namespace python {
 
diff --git a/python/google/protobuf/pyext/repeated_composite_container.h b/python/google/protobuf/pyext/repeated_composite_container.h
index 494db0ec..37f7b7e4 100644
--- a/python/google/protobuf/pyext/repeated_composite_container.h
+++ b/python/google/protobuf/pyext/repeated_composite_container.h
@@ -49,8 +49,9 @@ namespace protobuf {
 class FieldDescriptor;
 class Message;
 
+#ifdef _SHARED_PTR_H
 using std::shared_ptr;
-using std::string;
+#endif
 
 namespace python {
 
diff --git a/python/google/protobuf/pyext/repeated_scalar_container.h b/python/google/protobuf/pyext/repeated_scalar_container.h
index a13cf9b2..bd73017d 100644
--- a/python/google/protobuf/pyext/repeated_scalar_container.h
+++ b/python/google/protobuf/pyext/repeated_scalar_container.h
@@ -48,8 +48,9 @@ namespace protobuf {
 
 class Message;
 
+#ifdef _SHARED_PTR_H
 using std::shared_ptr;
-using std::string;
+#endif
 
 namespace python {
 
diff --git a/python/google/protobuf/pyext/scalar_map_container.h b/python/google/protobuf/pyext/scalar_map_container.h
index 8807892d..c055d1b5 100644
--- a/python/google/protobuf/pyext/scalar_map_container.h
+++ b/python/google/protobuf/pyext/scalar_map_container.h
@@ -45,8 +45,9 @@ namespace protobuf {
 
 class Message;
 
+#ifdef _SHARED_PTR_H
 using std::shared_ptr;
-using std::string;
+#endif
 
 namespace python {