diff --git a/dlls/user32/tests/win.c b/dlls/user32/tests/win.c
index a99163860f4..097aab64eaf 100644
--- a/dlls/user32/tests/win.c
+++ b/dlls/user32/tests/win.c
@@ -9282,7 +9282,8 @@ static void test_fullscreen(void)
         flush_events(TRUE);
 
         GetWindowRect(hwnd, &rc);
-        todo_wine
+        /* FVWM used by TestBots doesn't support _NET_WM_FULLSCREEN_MONITORS */
+        todo_wine_if(!EqualRect(&rc, &virtual_rect))
         ok(EqualRect(&rc, &virtual_rect), "Expected %s, got %s.\n",
            wine_dbgstr_rect(&virtual_rect), wine_dbgstr_rect(&rc));
         DestroyWindow(hwnd);
diff --git a/dlls/winex11.drv/display.c b/dlls/winex11.drv/display.c
index d53774f0e02..671c0c5dea2 100644
--- a/dlls/winex11.drv/display.c
+++ b/dlls/winex11.drv/display.c
@@ -533,6 +533,12 @@ void X11DRV_DisplayDevices_RegisterEventHandlers(void)
         handler->register_event_handlers();
 }
 
+/* Report whether a display device handler supports detecting dynamic device changes */
+BOOL X11DRV_DisplayDevices_SupportEventHandlers(void)
+{
+    return !!host_handler.register_event_handlers;
+}
+
 static BOOL force_display_devices_refresh;
 
 BOOL X11DRV_UpdateDisplayDevices( const struct gdi_device_manager *device_manager, BOOL force, void *param )
diff --git a/dlls/winex11.drv/window.c b/dlls/winex11.drv/window.c
index e1fa665608e..6bd028abb61 100644
--- a/dlls/winex11.drv/window.c
+++ b/dlls/winex11.drv/window.c
@@ -970,6 +970,46 @@ void update_user_time( Time time )
     XUnlockDisplay( gdi_display );
 }
 
+/* Update _NET_WM_FULLSCREEN_MONITORS when _NET_WM_STATE_FULLSCREEN is set to support fullscreen
+ * windows spanning multiple monitors */
+static void update_net_wm_fullscreen_monitors( struct x11drv_win_data *data )
+{
+    long monitors[4];
+    XEvent xev;
+
+    if (!(data->net_wm_state & (1 << NET_WM_STATE_FULLSCREEN)) || is_virtual_desktop())
+        return;
+
+    /* If the current display device handler can not detect dynamic device changes, do not use
+     * _NET_WM_FULLSCREEN_MONITORS because xinerama_get_fullscreen_monitors() may report wrong
+     * indices because of stale xinerama monitor information */
+    if (!X11DRV_DisplayDevices_SupportEventHandlers())
+        return;
+
+    if (!xinerama_get_fullscreen_monitors( &data->whole_rect, monitors ))
+        return;
+
+    if (!data->mapped)
+    {
+        XChangeProperty( data->display, data->whole_window, x11drv_atom(_NET_WM_FULLSCREEN_MONITORS),
+                         XA_CARDINAL, 32, PropModeReplace, (unsigned char *)monitors, 4 );
+    }
+    else
+    {
+        xev.xclient.type = ClientMessage;
+        xev.xclient.window = data->whole_window;
+        xev.xclient.message_type = x11drv_atom(_NET_WM_FULLSCREEN_MONITORS);
+        xev.xclient.serial = 0;
+        xev.xclient.display = data->display;
+        xev.xclient.send_event = True;
+        xev.xclient.format = 32;
+        xev.xclient.data.l[4] = 1;
+        memcpy( xev.xclient.data.l, monitors, sizeof(monitors) );
+        XSendEvent( data->display, root_window, False,
+                    SubstructureRedirectMask | SubstructureNotifyMask, &xev );
+    }
+}
+
 /***********************************************************************
  *     update_net_wm_states
  */
@@ -1051,6 +1091,7 @@ void update_net_wm_states( struct x11drv_win_data *data )
         }
     }
     data->net_wm_state = new_state;
+    update_net_wm_fullscreen_monitors( data );
 }
 
 /***********************************************************************
@@ -1143,6 +1184,7 @@ static void map_window( HWND hwnd, DWORD new_style )
 
         data->mapped = TRUE;
         data->iconic = (new_style & WS_MINIMIZE) != 0;
+        update_net_wm_fullscreen_monitors( data );
     }
     release_win_data( data );
 }
diff --git a/dlls/winex11.drv/x11drv.h b/dlls/winex11.drv/x11drv.h
index 5e1faf8a16e..a424eb112e8 100644
--- a/dlls/winex11.drv/x11drv.h
+++ b/dlls/winex11.drv/x11drv.h
@@ -479,6 +479,7 @@ enum x11drv_atoms
     XATOM__NET_SYSTEM_TRAY_OPCODE,
     XATOM__NET_SYSTEM_TRAY_S0,
     XATOM__NET_SYSTEM_TRAY_VISUAL,
+    XATOM__NET_WM_FULLSCREEN_MONITORS,
     XATOM__NET_WM_ICON,
     XATOM__NET_WM_MOVERESIZE,
     XATOM__NET_WM_NAME,
@@ -691,6 +692,7 @@ extern POINT virtual_screen_to_root( INT x, INT y ) DECLSPEC_HIDDEN;
 extern POINT root_to_virtual_screen( INT x, INT y ) DECLSPEC_HIDDEN;
 extern RECT get_host_primary_monitor_rect(void) DECLSPEC_HIDDEN;
 extern RECT get_work_area( const RECT *monitor_rect ) DECLSPEC_HIDDEN;
+extern BOOL xinerama_get_fullscreen_monitors( const RECT *rect, long *indices ) DECLSPEC_HIDDEN;
 extern void xinerama_init( unsigned int width, unsigned int height ) DECLSPEC_HIDDEN;
 extern void init_recursive_mutex( pthread_mutex_t *mutex ) DECLSPEC_HIDDEN;
 
@@ -803,6 +805,7 @@ extern BOOL get_host_primary_gpu(struct gdi_gpu *gpu) DECLSPEC_HIDDEN;
 extern void X11DRV_DisplayDevices_SetHandler(const struct x11drv_display_device_handler *handler) DECLSPEC_HIDDEN;
 extern void X11DRV_DisplayDevices_Init(BOOL force) DECLSPEC_HIDDEN;
 extern void X11DRV_DisplayDevices_RegisterEventHandlers(void) DECLSPEC_HIDDEN;
+extern BOOL X11DRV_DisplayDevices_SupportEventHandlers(void) DECLSPEC_HIDDEN;
 /* Display device handler used in virtual desktop mode */
 extern struct x11drv_display_device_handler desktop_handler DECLSPEC_HIDDEN;
 
diff --git a/dlls/winex11.drv/x11drv_main.c b/dlls/winex11.drv/x11drv_main.c
index 497e270ee8a..77e72752017 100644
--- a/dlls/winex11.drv/x11drv_main.c
+++ b/dlls/winex11.drv/x11drv_main.c
@@ -162,6 +162,7 @@ static const char * const atom_names[NB_XATOMS - FIRST_XATOM] =
     "_NET_SYSTEM_TRAY_OPCODE",
     "_NET_SYSTEM_TRAY_S0",
     "_NET_SYSTEM_TRAY_VISUAL",
+    "_NET_WM_FULLSCREEN_MONITORS",
     "_NET_WM_ICON",
     "_NET_WM_MOVERESIZE",
     "_NET_WM_NAME",
diff --git a/dlls/winex11.drv/xinerama.c b/dlls/winex11.drv/xinerama.c
index 847b8fb6efb..6835aa4a331 100644
--- a/dlls/winex11.drv/xinerama.c
+++ b/dlls/winex11.drv/xinerama.c
@@ -45,6 +45,7 @@ static MONITORINFOEXW default_monitor =
     { '\\','\\','.','\\','D','I','S','P','L','A','Y','1',0 }   /* szDevice */
 };
 
+static pthread_mutex_t xinerama_mutex = PTHREAD_MUTEX_INITIALIZER;
 static MONITORINFOEXW *monitors;
 static int nb_monitors;
 
@@ -122,6 +123,73 @@ static inline int query_screens(void)
 
 #endif  /* SONAME_LIBXINERAMA */
 
+/* Get xinerama monitor indices required for _NET_WM_FULLSCREEN_MONITORS */
+BOOL xinerama_get_fullscreen_monitors( const RECT *rect, long *indices )
+{
+    RECT window_rect, intersected_rect, monitor_rect;
+    BOOL ret = FALSE;
+    POINT offset;
+    INT i;
+
+    pthread_mutex_lock( &xinerama_mutex );
+    if (nb_monitors == 1)
+    {
+        memset( indices, 0, sizeof(*indices) * 4 );
+        ret = TRUE;
+        goto done;
+    }
+
+    /* Convert window rectangle to root coordinates */
+    offset = virtual_screen_to_root( rect->left, rect->top );
+    window_rect.left = offset.x;
+    window_rect.top = offset.y;
+    window_rect.right = window_rect.left + rect->right - rect->left;
+    window_rect.bottom = window_rect.top + rect->bottom - rect->top;
+
+    /* Compare to xinerama monitor rectangles in root coordinates */
+    offset.x = INT_MAX;
+    offset.y = INT_MAX;
+    for (i = 0; i < nb_monitors; ++i)
+    {
+        offset.x = min( offset.x, monitors[i].rcMonitor.left );
+        offset.y = min( offset.y, monitors[i].rcMonitor.top );
+    }
+
+    indices[0] = -1;
+    indices[1] = -1;
+    indices[2] = -1;
+    indices[3] = -1;
+    for (i = 0; i < nb_monitors; ++i)
+    {
+        SetRect( &monitor_rect, monitors[i].rcMonitor.left - offset.x,
+                 monitors[i].rcMonitor.top - offset.y, monitors[i].rcMonitor.right - offset.x,
+                 monitors[i].rcMonitor.bottom - offset.y );
+        intersect_rect( &intersected_rect, &window_rect, &monitor_rect );
+        if (EqualRect( &intersected_rect, &monitor_rect ))
+        {
+            if (indices[0] == -1 || monitors[i].rcMonitor.top < monitors[indices[0]].rcMonitor.top)
+                indices[0] = i;
+            if (indices[1] == -1 || monitors[i].rcMonitor.bottom > monitors[indices[1]].rcMonitor.bottom)
+                indices[1] = i;
+            if (indices[2] == -1 || monitors[i].rcMonitor.left < monitors[indices[2]].rcMonitor.left)
+                indices[2] = i;
+            if (indices[3] == -1 || monitors[i].rcMonitor.right > monitors[indices[3]].rcMonitor.right)
+                indices[3] = i;
+        }
+    }
+
+    if (indices[0] == -1 || indices[1] == -1 || indices[2] == -1 || indices[3] == -1)
+        ERR("Failed to get xinerama fullscreen monitor indices.\n");
+    else
+        ret = TRUE;
+
+done:
+    pthread_mutex_unlock( &xinerama_mutex );
+    if (ret)
+        TRACE( "fullsceen monitors: %ld,%ld,%ld,%ld.\n", indices[0], indices[1], indices[2], indices[3] );
+    return ret;
+}
+
 static BOOL xinerama_get_gpus( struct gdi_gpu **new_gpus, int *count )
 {
     static const WCHAR wine_adapterW[] = {'W','i','n','e',' ','A','d','a','p','t','e','r',0};
@@ -157,9 +225,13 @@ static BOOL xinerama_get_adapters( ULONG_PTR gpu_id, struct gdi_adapter **new_ad
         return FALSE;
 
     /* Being lazy, actual adapter count may be less */
+    pthread_mutex_lock( &xinerama_mutex );
     adapters = calloc( nb_monitors, sizeof(*adapters) );
     if (!adapters)
+    {
+        pthread_mutex_unlock( &xinerama_mutex );
         return FALSE;
+    }
 
     primary_index = primary_monitor;
     if (primary_index >= nb_monitors)
@@ -204,6 +276,7 @@ static BOOL xinerama_get_adapters( ULONG_PTR gpu_id, struct gdi_adapter **new_ad
 
     *new_adapters = adapters;
     *count = index;
+    pthread_mutex_unlock( &xinerama_mutex );
     return TRUE;
 }
 
@@ -223,6 +296,8 @@ static BOOL xinerama_get_monitors( ULONG_PTR adapter_id, struct gdi_monitor **ne
     INT index = 0;
     INT i;
 
+    pthread_mutex_lock( &xinerama_mutex );
+
     for (i = first; i < nb_monitors; i++)
     {
         if (i == first
@@ -233,7 +308,10 @@ static BOOL xinerama_get_monitors( ULONG_PTR adapter_id, struct gdi_monitor **ne
 
     monitor = calloc( monitor_count, sizeof(*monitor) );
     if (!monitor)
+    {
+        pthread_mutex_unlock( &xinerama_mutex );
         return FALSE;
+    }
 
     for (i = first; i < nb_monitors; i++)
     {
@@ -257,6 +335,7 @@ static BOOL xinerama_get_monitors( ULONG_PTR adapter_id, struct gdi_monitor **ne
 
     *new_monitors = monitor;
     *count = monitor_count;
+    pthread_mutex_unlock( &xinerama_mutex );
     return TRUE;
 }
 
@@ -275,6 +354,8 @@ void xinerama_init( unsigned int width, unsigned int height )
     if (is_virtual_desktop())
         return;
 
+    pthread_mutex_lock( &xinerama_mutex );
+
     SetRect( &rect, 0, 0, width, height );
     if (!query_screens())
     {
@@ -298,6 +379,8 @@ void xinerama_init( unsigned int width, unsigned int height )
                (monitors[i].dwFlags & MONITORINFOF_PRIMARY) ? " (primary)" : "" );
     }
 
+    pthread_mutex_unlock( &xinerama_mutex );
+
     handler.name = "Xinerama";
     handler.priority = 100;
     handler.get_gpus = xinerama_get_gpus;
diff --git a/dlls/winex11.drv/xrandr.c b/dlls/winex11.drv/xrandr.c
index 2b75e3b28eb..b4d613cf56a 100644
--- a/dlls/winex11.drv/xrandr.c
+++ b/dlls/winex11.drv/xrandr.c
@@ -1190,6 +1190,8 @@ static void xrandr14_free_monitors( struct gdi_monitor *monitors, int count )
 
 static BOOL xrandr14_device_change_handler( HWND hwnd, XEvent *event )
 {
+    RECT rect;
+
     xrandr14_invalidate_current_mode_cache();
     if (hwnd == NtUserGetDesktopWindow() && NtUserGetWindowThread( hwnd, NULL ) == GetCurrentThreadId())
     {
@@ -1197,6 +1199,9 @@ static BOOL xrandr14_device_change_handler( HWND hwnd, XEvent *event )
         init_registry_display_settings();
         X11DRV_resize_desktop();
     }
+    /* Update xinerama monitors for xinerama_get_fullscreen_monitors() */
+    rect = get_host_primary_monitor_rect();
+    xinerama_init( rect.right - rect.left, rect.bottom - rect.top );
     return FALSE;
 }