diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
index ba32da2fa4..ded531394e 100644
--- a/hw/m68k/q800.c
+++ b/hw/m68k/q800.c
@@ -560,9 +560,9 @@ static void q800_machine_init(MachineState *machine)
                             TYPE_NUBUS_MACFB);
     dev = DEVICE(&m->macfb);
     qdev_prop_set_uint32(dev, "slot", 9);
-    qdev_prop_set_uint32(dev, "width", graphic_width);
-    qdev_prop_set_uint32(dev, "height", graphic_height);
-    qdev_prop_set_uint8(dev, "depth", graphic_depth);
+    qdev_prop_set_uint32(dev, "width", graphic_width ?: 800);
+    qdev_prop_set_uint32(dev, "height", graphic_height ?: 600);
+    qdev_prop_set_uint8(dev, "depth", graphic_depth ?: 8);
     qdev_realize(dev, BUS(nubus), &error_fatal);
 
     macfb_mode = (NUBUS_MACFB(dev)->macfb).mode;
diff --git a/system/globals-target.c b/system/globals-target.c
index 989720591e..e3f7d846ac 100644
--- a/system/globals-target.c
+++ b/system/globals-target.c
@@ -14,9 +14,9 @@ int graphic_width = 1024;
 int graphic_height = 768;
 int graphic_depth = 8;
 #elif defined(TARGET_M68K)
-int graphic_width = 800;
-int graphic_height = 600;
-int graphic_depth = 8;
+int graphic_width;
+int graphic_height;
+int graphic_depth;
 #else
 int graphic_width = 800;
 int graphic_height = 600;