diff --git a/dix/dispatch.c b/dix/dispatch.c
index 43cb4d1d3..4a4481ab3 100644
--- a/dix/dispatch.c
+++ b/dix/dispatch.c
@@ -3898,6 +3898,8 @@ AddScreen(
 	return -1;
     }
 
+    update_desktop_dimensions();
+
     dixRegisterScreenPrivateKey(&cursorScreenDevPriv, pScreen, PRIVATE_CURSOR, 0);
 
     return i;
diff --git a/dix/inpututils.c b/dix/inpututils.c
index eeae2a74f..8a834442c 100644
--- a/dix/inpututils.c
+++ b/dix/inpututils.c
@@ -628,6 +628,30 @@ point_on_screen(ScreenPtr pScreen, int x, int y)
 }
 
 /**
+ * Update desktop dimensions on the screenInfo struct.
+ */
+void
+update_desktop_dimensions(void)
+{
+    int i;
+    int x1 = INT_MAX, y1 = INT_MAX; /* top-left */
+    int x2 = INT_MIN, y2 = INT_MIN; /* bottom-right */
+
+    for (i = 0; i < screenInfo.numScreens; i++) {
+        ScreenPtr screen = screenInfo.screens[i];
+        x1 = min(x1, screen->x);
+        y1 = min(y1, screen->y);
+        x2 = max(x2, screen->x + screen->width);
+        y2 = max(y2, screen->y + screen->height);
+    }
+
+    screenInfo.x = x1;
+    screenInfo.y = y1;
+    screenInfo.width = x2 - x1;
+    screenInfo.height = y2 - y1;
+}
+
+/*
  * Delete the element with the key from the list, freeing all memory
  * associated with the element..
  */
diff --git a/hw/xfree86/common/xf86Cursor.c b/hw/xfree86/common/xf86Cursor.c
index 929f047cc..6f5d726f0 100644
--- a/hw/xfree86/common/xf86Cursor.c
+++ b/hw/xfree86/common/xf86Cursor.c
@@ -838,6 +838,8 @@ xf86InitOrigins(void)
 		FillOutEdge(pLayout->down, pScreen->width);
 	}
     }
+
+    update_desktop_dimensions();
 }
 
 void
diff --git a/hw/xfree86/common/xf86RandR.c b/hw/xfree86/common/xf86RandR.c
index 4663d0366..d0e47841e 100644
--- a/hw/xfree86/common/xf86RandR.c
+++ b/hw/xfree86/common/xf86RandR.c
@@ -313,6 +313,9 @@ xf86RandRSetConfig (ScreenPtr		pScreen,
 	return FALSE;
     }
 
+
+    update_desktop_dimensions();
+
     /*
      * Move the cursor back where it belongs; SwitchMode repositions it
      * FIXME: duplicated code, see modes/xf86RandR12.c
diff --git a/hw/xfree86/modes/xf86RandR12.c b/hw/xfree86/modes/xf86RandR12.c
index cb20d1c35..d5031a2f1 100644
--- a/hw/xfree86/modes/xf86RandR12.c
+++ b/hw/xfree86/modes/xf86RandR12.c
@@ -736,6 +736,8 @@ xf86RandR12ScreenSetSize (ScreenPtr	pScreen,
     xf86SetViewport (pScreen, 0, 0);
 
 finish:
+    update_desktop_dimensions();
+
     if (pRoot && pScrn->vtSema)
 	(*pScrn->EnableDisableFBAccess) (pScreen->myNum, TRUE);
 #if RANDR_12_INTERFACE
diff --git a/include/input.h b/include/input.h
index b7de5ca3d..2544996a6 100644
--- a/include/input.h
+++ b/include/input.h
@@ -609,5 +609,6 @@ extern _X_EXPORT void input_option_set_key(InputOption *opt, const char* key);
 extern _X_EXPORT void input_option_set_value(InputOption *opt, const char* value);
 
 extern _X_HIDDEN Bool point_on_screen(ScreenPtr pScreen, int x, int y);
+extern _X_HIDDEN void update_desktop_dimensions(void);
 
 #endif /* INPUT_H */
diff --git a/include/scrnintstr.h b/include/scrnintstr.h
index a9357e8a5..132a67193 100644
--- a/include/scrnintstr.h
+++ b/include/scrnintstr.h
@@ -561,6 +561,10 @@ typedef struct _ScreenInfo {
 		formats[MAXFORMATS];
     int		numScreens;
     ScreenPtr	screens[MAXSCREENS];
+    int         x;      /* origin */
+    int         y;      /* origin */
+    int		width;  /* total width of all screens together */
+    int		height; /* total height of all screens together */
 } ScreenInfo;
 
 extern _X_EXPORT ScreenInfo screenInfo;
diff --git a/test/misc.c b/test/misc.c
index 3d3b1a1e3..d98449ba0 100644
--- a/test/misc.c
+++ b/test/misc.c
@@ -27,6 +27,9 @@
 
 #include <stdint.h>
 #include "misc.h"
+#include "scrnintstr.h"
+
+ScreenInfo screenInfo;
 
 static void dix_version_compare(void)
 {
@@ -54,9 +57,110 @@ static void dix_version_compare(void)
     assert(rc < 0);
 }
 
+static void dix_update_desktop_dimensions(void)
+{
+    int i;
+    int x, y, w, h;
+    int w2, h2;
+    ScreenRec screens[MAXSCREENS];
+
+    for (i = 0; i < MAXSCREENS; i++)
+        screenInfo.screens[i] = &screens[i];
+
+    x = 0;
+    y = 0;
+    w = 10;
+    h = 5;
+    w2 = 35;
+    h2 = 25;
+
+#define assert_dimensions(_x, _y, _w, _h) \
+    update_desktop_dimensions();          \
+    printf("%d %d %d %d\n", screenInfo.x, screenInfo.y, screenInfo.width, screenInfo.height); \
+    assert(screenInfo.x == _x);           \
+    assert(screenInfo.y == _y);           \
+    assert(screenInfo.width == _w);       \
+    assert(screenInfo.height == _h);
+
+#define set_screen(idx, _x, _y, _w, _h)   \
+    screenInfo.screens[idx]->x = _x;      \
+    screenInfo.screens[idx]->y = _y;      \
+    screenInfo.screens[idx]->width = _w;  \
+    screenInfo.screens[idx]->height = _h; \
+
+    printf("Testing\n");
+
+    /* single screen */
+    screenInfo.numScreens = 1;
+    set_screen(0, x, y, w, h);
+    assert_dimensions(x, y, w, h);
+
+    /* dualhead rightof */
+    screenInfo.numScreens = 2;
+    set_screen(1, w, 0, w2, h2);
+    assert_dimensions(x, y, w + w2, h2);
+
+    /* dualhead belowof */
+    screenInfo.numScreens = 2;
+    set_screen(1, 0, h, w2, h2);
+    assert_dimensions(x, y, w2, h + h2);
+
+    /* triplehead L shape */
+    screenInfo.numScreens = 3;
+    set_screen(1, 0, h, w2, h2);
+    set_screen(2, w2, h2, w, h);
+    assert_dimensions(x, y, w + w2, h + h2);
+
+    /* quadhead 2x2 */
+    screenInfo.numScreens = 4;
+    set_screen(1, 0, h, w, h);
+    set_screen(2, w, h, w, h2);
+    set_screen(3, w, 0, w2, h);
+    assert_dimensions(x, y, w + w2, h + h2);
+
+    /* quadhead horiz line */
+    screenInfo.numScreens = 4;
+    set_screen(1, w, 0, w, h);
+    set_screen(2, 2 * w, 0, w, h);
+    set_screen(3, 3 * w, 0, w, h);
+    assert_dimensions(x, y, 4 * w, h);
+
+    /* quadhead vert line */
+    screenInfo.numScreens = 4;
+    set_screen(1, 0, h, w, h);
+    set_screen(2, 0, 2 * h, w, h);
+    set_screen(3, 0, 3 * h, w, h);
+    assert_dimensions(x, y, w, 4 * h);
+
+
+    /* x overlap */
+    screenInfo.numScreens = 2;
+    set_screen(0, 0, 0, w2, h2);
+    set_screen(1, w, 0, w2, h2);
+    assert_dimensions(x, y, w2 + w, h2);
+
+    /* y overlap */
+    screenInfo.numScreens = 2;
+    set_screen(0, 0, 0, w2, h2);
+    set_screen(1, 0, h, w2, h2);
+    assert_dimensions(x, y, w2, h2 + h);
+
+    /* negative origin */
+    screenInfo.numScreens = 1;
+    set_screen(0, -w2, -h2, w, h);
+    assert_dimensions(-w2, -h2, w, h);
+
+    /* dualhead negative origin, overlap */
+    screenInfo.numScreens = 2;
+    set_screen(0, -w2, -h2, w2, h2);
+    set_screen(1, -w, -h, w, h);
+    assert_dimensions(-w2, -h2, w2, h2);
+}
+
 int main(int argc, char** argv)
 {
     dix_version_compare();
+    dix_update_desktop_dimensions();
 
     return 0;
 }