diff --git a/src/frontend/terminaloverlay.cc b/src/frontend/terminaloverlay.cc
index c7e0f5e..cd28f50 100644
--- a/src/frontend/terminaloverlay.cc
+++ b/src/frontend/terminaloverlay.cc
@@ -172,7 +172,7 @@ NotificationEngine::NotificationEngine()
     show_quit_keystroke( true )
 {}
 
-static std::string human_readable_duration( int num_seconds, const std::string seconds_abbr ) {
+static std::string human_readable_duration( int num_seconds, const std::string &seconds_abbr ) {
   char tmp[ 128 ];
   if ( num_seconds < 60 ) {
     snprintf( tmp, 128, "%d %s", num_seconds, seconds_abbr.c_str() );
diff --git a/src/terminal/terminaldisplay.h b/src/terminal/terminaldisplay.h
index acd0fc4..028f62e 100644
--- a/src/terminal/terminaldisplay.h
+++ b/src/terminal/terminaldisplay.h
@@ -58,7 +58,7 @@ namespace Terminal {
     }
 
     void append( const char * s ) { str.append( s ); }
-    void appendstring( const std::string s ) { str.append( s ); }
+    void appendstring( const std::string &s ) { str.append( s ); }
 
     void append_silent_move( int y, int x );
   };