diff --git a/src/google/protobuf/descriptor.cc b/src/google/protobuf/descriptor.cc
index 7af37c57f3..03c4e2b516 100644
--- a/src/google/protobuf/descriptor.cc
+++ b/src/google/protobuf/descriptor.cc
@@ -1090,7 +1090,7 @@ inline void DescriptorPool::Tables::FindAllExtensions(
 
 bool DescriptorPool::Tables::AddSymbol(const std::string& full_name,
                                        Symbol symbol) {
-  if (InsertIfNotPresent(&symbols_by_name_, full_name.c_str(), symbol)) {
+  if (InsertIfNotPresent(&symbols_by_name_, full_name, symbol)) {
     symbols_after_checkpoint_.push_back(full_name.c_str());
     return true;
   } else {
@@ -1106,7 +1106,7 @@ bool FileDescriptorTables::AddAliasUnderParent(const void* parent,
 }
 
 bool DescriptorPool::Tables::AddFile(const FileDescriptor* file) {
-  if (InsertIfNotPresent(&files_by_name_, file->name().c_str(), file)) {
+  if (InsertIfNotPresent(&files_by_name_, file->name(), file)) {
     files_after_checkpoint_.push_back(file->name().c_str());
     return true;
   } else {
@@ -2626,6 +2626,8 @@ void Descriptor::DebugString(int depth, std::string* contents,
       const Descriptor::ReservedRange* range = reserved_range(i);
       if (range->end == range->start + 1) {
         strings::SubstituteAndAppend(contents, "$0, ", range->start);
+      } else if (range->end > FieldDescriptor::kMaxNumber) {
+        strings::SubstituteAndAppend(contents, "$0 to max, ", range->start);
       } else {
         strings::SubstituteAndAppend(contents, "$0 to $1, ", range->start,
                                   range->end - 1);
@@ -2829,6 +2831,8 @@ void EnumDescriptor::DebugString(
       const EnumDescriptor::ReservedRange* range = reserved_range(i);
       if (range->end == range->start) {
         strings::SubstituteAndAppend(contents, "$0, ", range->start);
+      } else if (range->end == INT_MAX) {
+        strings::SubstituteAndAppend(contents, "$0 to max, ", range->start);
       } else {
         strings::SubstituteAndAppend(contents, "$0 to $1, ", range->start,
                                   range->end);
@@ -4019,6 +4023,11 @@ bool DescriptorBuilder::AddSymbol(const std::string& full_name,
   // Use its file as the parent instead.
   if (parent == nullptr) parent = file_;
 
+  if (full_name.find('\0') != std::string::npos) {
+    AddError(full_name, proto, DescriptorPool::ErrorCollector::NAME,
+             "\"" + full_name + "\" contains null character.");
+    return false;
+  }
   if (tables_->AddSymbol(full_name, symbol)) {
     if (!file_tables_->AddAliasUnderParent(parent, name, symbol)) {
       // This is only possible if there was already an error adding something of
@@ -4059,6 +4068,11 @@ bool DescriptorBuilder::AddSymbol(const std::string& full_name,
 void DescriptorBuilder::AddPackage(const std::string& name,
                                    const Message& proto,
                                    const FileDescriptor* file) {
+  if (name.find('\0') != std::string::npos) {
+    AddError(name, proto, DescriptorPool::ErrorCollector::NAME,
+             "\"" + name + "\" contains null character.");
+    return;
+  }
   if (tables_->AddSymbol(name, Symbol(file))) {
     // Success.  Also add parent package, if any.
     std::string::size_type dot_pos = name.find_last_of('.');
@@ -4372,6 +4386,12 @@ FileDescriptor* DescriptorBuilder::BuildFileImpl(
   }
   result->pool_ = pool_;
 
+  if (result->name().find('\0') != std::string::npos) {
+    AddError(result->name(), proto, DescriptorPool::ErrorCollector::NAME,
+             "\"" + result->name() + "\" contains null character.");
+    return nullptr;
+  }
+
   // Add to tables.
   if (!tables_->AddFile(result)) {
     AddError(proto.name(), proto, DescriptorPool::ErrorCollector::OTHER,