diff --git a/CGDOOM-minisdk/CGDOOM/platform.h b/CGDOOM-minisdk/CGDOOM/platform.h
index 834365d..9a514af 100644
--- a/CGDOOM-minisdk/CGDOOM/platform.h
+++ b/CGDOOM-minisdk/CGDOOM/platform.h
@@ -53,6 +53,29 @@ enum {
    disable.) */
 #define CGDOOM_DIRECT_R61524
 
+//---
+// Memory distribution
+//---
+
+/* When direct-display access is disabled, put the screens in secondary VRAM
+   and use VRAM for rendering. When it's enabled, put the screens in VRAM and
+   use the secondary VRAM as heap. We swap because using the VRAM as heap would
+   cause problems with error screens (stepping through errors would crash). */
+#ifdef CGDOOM_DIRECT_R61524
+# define CGDOOM_SCREENS_BASE ((void *)GetVRAMAddress())
+#else
+# define CGDOOM_SCREENS_BASE SaveVRAMBuffer
+#endif
+
+/* The primary/secondary VRAM covers 384*216*2 = 162 kiB:
+   -> Give 320*200 = 64 kB to screens[0] (main display)
+   -> Give 320*200 = 64 kB to screens[1] (intermissions)
+   -> Give 320*32  = 10 kiB to screens[4] (status bar)
+   -> 27 kiB are left */
+#define CGDOOM_SCREENS_0 (CGDOOM_SCREENS_BASE)
+#define CGDOOM_SCREENS_1 (CGDOOM_SCREENS_BASE + 320*200)
+#define CGDOOM_SCREENS_4 (CGDOOM_SCREENS_BASE + 320*200*2)
+
 //---
 
 #include "keyboard.hpp"
diff --git a/README b/README
index 06840af..ea88bbd 100644
--- a/README
+++ b/README
@@ -19,13 +19,12 @@ UI improvements TODO:
 WAD support TODO:
 -> Unmodified 1.9 shareware WAD works all the way through?
 -> Shareware WAD from Planète Casio should work 100%
--> Ultimate DOOM WAD runs out of memory in E1M6, otherwise should work
+-> Ultimate Doom WAD should work 100% for episode 1
 
 Technical support TODO:
 -> Supply more VRAM memory to internal allocator
    => Merge internal heap into Z_Zone? (< 50 kB)
    => Rewrite video code to use long PRAM0 access? (138 kB)
-   => Use the XRAM/R61524 combo and use VRAM as heap? (160 kB)
 -> Rate-limit the game when overclocking
 -> Load/Save game would be very cool
 -> Reenable LTO if possible
diff --git a/cgdoom/i_system.c b/cgdoom/i_system.c
index ca888bb..3680089 100644
--- a/cgdoom/i_system.c
+++ b/cgdoom/i_system.c
@@ -75,6 +75,15 @@ byte* I_ZoneBase (int*	size, int i)
         *size = &eextra - &sextra;
         return &sextra;
     }
+#ifdef CGDOOM_DIRECT_R61524
+    if (i == 2)
+    {
+        /* Secondary VRAM (screen buffers being in the main VRAM because we're
+           doing direct access so we don't need Bdisp_PutDisp_DD() */
+        *size = 384 * 216 * 2;
+        return SaveVRAMBuffer;
+    }
+#endif
     return NULL;
 }
 
diff --git a/cgdoom/st_stuff.c b/cgdoom/st_stuff.c
index 63a0088..baf56c9 100644
--- a/cgdoom/st_stuff.c
+++ b/cgdoom/st_stuff.c
@@ -1114,5 +1114,5 @@ void ST_Init (void)
 {
   veryfirsttime = 0;
   ST_loadData();
-  screens[4] = SaveVRAMBuffer + 2 * SCREENWIDTH * SCREENHEIGHT;
+  screens[4] = CGDOOM_SCREENS_4;
 }
diff --git a/cgdoom/v_video.c b/cgdoom/v_video.c
index 64de3aa..951b1a0 100644
--- a/cgdoom/v_video.c
+++ b/cgdoom/v_video.c
@@ -352,9 +352,9 @@ void V_GetBlock( int  x, int  y, int  scrn, int  width, int  height, byte*  dest
 void V_Init (void) 
 { 
   /* screens[0] is the main screen */
-  screens[0] = SaveVRAMBuffer;
+  screens[0] = CGDOOM_SCREENS_0;
   /* screens[1] is used for the level end sequence (intermission) */
-  screens[1] = SaveVRAMBuffer + SCREENWIDTH * SCREENHEIGHT;
+  screens[1] = CGDOOM_SCREENS_1;
   /* screens[2] and screens[3] are used for wipe effects (disabled here) */
   /* screens[4] is used for the status bar (allocated by st_stuff.c) */