diff --git a/src/unix/fontutil.cpp b/src/unix/fontutil.cpp
index 97f7fb4ae3..2ba48b9182 100644
--- a/src/unix/fontutil.cpp
+++ b/src/unix/fontutil.cpp
@@ -795,8 +795,13 @@ wxFontEncoding wxNativeFontInfo::GetEncoding() const
 
 void wxNativeFontInfo::SetFractionalPointSize(float pointsize)
 {
-    SetXFontComponent(wxXLFD_POINTSIZE,
-                      wxString::Format("%d", wxRound(10*pointsize)));
+    wxString s;
+    if ( pointsize < 0 )
+        s = '*';
+    else
+        s.Printf("%d", wxRound(10*pointsize));
+
+    SetXFontComponent(wxXLFD_POINTSIZE, s);
 }
 
 void wxNativeFontInfo::SetStyle(wxFontStyle style)