diff --git a/src/drivers/X11/Fl_X11_Screen_Driver.cxx b/src/drivers/X11/Fl_X11_Screen_Driver.cxx
index f8bf520b1..f9bae70f2 100644
--- a/src/drivers/X11/Fl_X11_Screen_Driver.cxx
+++ b/src/drivers/X11/Fl_X11_Screen_Driver.cxx
@@ -274,13 +274,14 @@ typedef struct {
 typedef XRRScreenSize* (*XRRSizes_type)(Display *dpy, int screen, int *nsizes);
 #endif // USE_XRANDR
 
-void Fl_X11_Screen_Driver::init()
-{
+void Fl_X11_Screen_Driver::init() {
   if (!fl_display) open_display();
-  
+
   int dpi_by_randr = 0;
   float dpih = 0.0f, dpiv = 0.0f;
+
 #if USE_XRANDR
+
   static XRRSizes_type XRRSizes_f = NULL;
   if (!XRRSizes_f) {
     void *libxrandr_addr = dlopen("libXrandr.so.2", RTLD_LAZY);
@@ -293,17 +294,24 @@ void Fl_X11_Screen_Driver::init()
   if (XRRSizes_f) {
     int nscreens;
     XRRScreenSize *ssize = XRRSizes_f(fl_display, fl_screen, &nscreens);
-    //    for(int i=0;i<nscreens;i++)
-    //      printf("width=%d height=%d mwidth=%d mheight=%d\n",ssize[i].width,ssize[i].height,ssize[i].mwidth,ssize[i].mheight);
-    int mm = ssize[0].mwidth;
-    dpih = mm ? ssize[0].width*25.4f/mm : 0.0f;
-    mm = ssize[0].mheight;
-    dpiv = mm ? ssize[0].height*25.4f/mm : 0.0f;
-    dpi_by_randr = 1;
+
+    //for (int i=0; i<nscreens; i++)
+    //  printf("width=%d height=%d mwidth=%d mheight=%d\n",
+    //         ssize[i].width,ssize[i].height,ssize[i].mwidth,ssize[i].mheight);
+
+    if (nscreens > 0) { // Note: XRRSizes() *may* return nscreens == 0, see docs
+      int mm = ssize[0].mwidth;
+      dpih = mm ? ssize[0].width*25.4f/mm : 0.0f;
+      mm = ssize[0].mheight;
+      dpiv = mm ? ssize[0].height*25.4f/mm : 0.0f;
+      dpi_by_randr = 1;
+    }
   }
+
 #endif // USE_XRANDR
 
 #if HAVE_XINERAMA
+
   if (XineramaIsActive(fl_display)) {
     XineramaScreenInfo *xsi = XineramaQueryScreens(fl_display, &num_screens);
     if (num_screens > MAX_SCREENS) num_screens = MAX_SCREENS;
@@ -315,8 +323,10 @@ void Fl_X11_Screen_Driver::init()
       screens[i].width = xsi[i].width;
       screens[i].height = xsi[i].height;
 
-      if (dpi_by_randr) { dpi[i][0] = dpih; dpi[i][1] = dpiv; }
-      else {
+      if (dpi_by_randr) {
+	dpi[i][0] = dpih;
+	dpi[i][1] = dpiv;
+      } else {
         int mm = DisplayWidthMM(fl_display, fl_screen);
         dpi[i][0] = mm ? screens[i].width*25.4f/mm : 0.0f;
         mm = DisplayHeightMM(fl_display, fl_screen);
@@ -325,23 +335,27 @@ void Fl_X11_Screen_Driver::init()
     }
     if (xsi) XFree(xsi);
   } else
-#endif
-  { // ! XineramaIsActive()
+
+#endif // HAVE_XINERAMA
+
+  { // ! HAVE_XINERAMA || ! XineramaIsActive()
     num_screens = ScreenCount(fl_display);
     if (num_screens > MAX_SCREENS) num_screens = MAX_SCREENS;
-   
+
     for (int i=0; i<num_screens; i++) {
       screens[i].x_org = 0;
       screens[i].y_org = 0;
       screens[i].width = DisplayWidth(fl_display, i);
       screens[i].height = DisplayHeight(fl_display, i);
- 
-      if (dpi_by_randr) { dpi[i][0] = dpih; dpi[i][1] = dpiv; }
-      else {
-        int mm = DisplayWidthMM(fl_display, fl_screen);
-        dpi[i][0] = mm ? screens[i].width*25.4f/mm : 0.0f;
-        mm = DisplayHeightMM(fl_display, fl_screen);
-        dpi[i][1] = mm ? screens[i].height*25.4f/mm : 0.0f;
+
+      if (dpi_by_randr) {
+	dpi[i][0] = dpih;
+	dpi[i][1] = dpiv;
+      } else {
+	int mm = DisplayWidthMM(fl_display, i);
+	dpi[i][0] = mm ? screens[i].width*25.4f/mm : 0.0f;
+	mm = DisplayHeightMM(fl_display, fl_screen);
+	dpi[i][1] = mm ? screens[i].height*25.4f/mm : 0.0f;
       }
     }
   }