diff --git a/src/lib/dns/master_lexer_inputsource.cc b/src/lib/dns/master_lexer_inputsource.cc
index f38d6c3a53..6c43dc1c56 100644
--- a/src/lib/dns/master_lexer_inputsource.cc
+++ b/src/lib/dns/master_lexer_inputsource.cc
@@ -46,7 +46,7 @@ InputSource::InputSource(const char* filename) :
     name_(filename),
     input_(file_stream_)
 {
-    file_stream_.open(filename, std::fstream::in);
+    file_stream_.open(filename);
     if (file_stream_.fail()) {
         isc_throw(OpenError,
                   "Error opening the input source file: " << filename);
diff --git a/src/lib/dns/master_lexer_inputsource.h b/src/lib/dns/master_lexer_inputsource.h
index b7eee5f11c..136e8097a8 100644
--- a/src/lib/dns/master_lexer_inputsource.h
+++ b/src/lib/dns/master_lexer_inputsource.h
@@ -135,7 +135,7 @@ private:
     size_t buffer_pos_;
 
     const std::string name_;
-    std::fstream file_stream_;
+    std::ifstream file_stream_;
     std::istream& input_;
 };