diff --git a/qt/formatter.cc b/qt/formatter.cc
index de11d237b..6c056ec90 100644
--- a/qt/formatter.cc
+++ b/qt/formatter.cc
@@ -92,9 +92,11 @@ Speed :: fromKBps( double KBps )
 ***/
 
 QString
-Formatter :: memToString( uint64_t bytes )
+Formatter :: memToString( int64_t bytes )
 {
-    if( !bytes )
+    if( bytes < 1 )
+        return tr( "Unknown" );
+    else if( !bytes )
         return tr( "None" );
     else {
         char buf[128];
@@ -104,9 +106,11 @@ Formatter :: memToString( uint64_t bytes )
 }
 
 QString
-Formatter :: sizeToString( uint64_t bytes )
+Formatter :: sizeToString( int64_t bytes )
 {
-    if( !bytes )
+    if( bytes < 1 )
+        return tr( "Unknown" );
+    else if( !bytes )
         return tr( "None" );
     else {
         char buf[128];
diff --git a/qt/formatter.h b/qt/formatter.h
index 51d9375ef..de8b76f21 100644
--- a/qt/formatter.h
+++ b/qt/formatter.h
@@ -32,8 +32,8 @@ class Formatter: public QObject
 
     public:
 
-        static QString memToString( uint64_t bytes );
-        static QString sizeToString( uint64_t bytes );
+        static QString memToString( int64_t bytes );
+        static QString sizeToString( int64_t bytes );
         static QString speedToString( const Speed& speed );
         static QString percentToString( double x );
         static QString ratioToString( double ratio );