diff --git a/README.md b/README.md
index a506a7f..123a205 100644
--- a/README.md
+++ b/README.md
@@ -111,11 +111,11 @@ There are a couple types used that are specific to f00bar.
 | border        | dict   | no   | Configures a border around the status bar
 | border.width  | int    | no   | Width, in pixels, of the border
 | border.color  | color  | no   | The color of the border
-| border.margin | int    | no   | left/rigth/top/bottom margins, from screen edge to bar
-| border.left-margin | int | no | left margin from screen edge to bar. Overrides `border.margin`
-| border.right-margin | int | no | right margin from screen edge to bar. Overrides `border.margin`
-| border.top-margin | int | no | top margin from screen edge to bar. Overrides `border.margin`
-| border.bottom-margin | int | no | bottom margin from screen edge to bar. Overrides `border.margin`
+| border.margin | int    | no   | left/rigth/top/bottom margins, from screen edge to bar. _Wayland only_
+| border.left-margin | int | no | left margin from screen edge to bar. Overrides `border.margin`. _Wayland only_
+| border.right-margin | int | no | right margin from screen edge to bar. Overrides `border.margin`. _Wayland only_
+| border.top-margin | int | no | top margin from screen edge to bar. Overrides `border.margin`. _Wayland only_
+| border.bottom-margin | int | no | bottom margin from screen edge to bar. Overrides `border.margin`. _Wayland only_
 | font          | font   | no   | Default font to use in modules and particles
 | foreground    | color  | no   | Default foreground (text) color to use
 | left          | list   | no   | Left-aligned modules
diff --git a/bar/wayland.c b/bar/wayland.c
index b7cda6c..0d06f4a 100644
--- a/bar/wayland.c
+++ b/bar/wayland.c
@@ -656,6 +656,7 @@ setup(struct bar *_bar)
         return false;
     }
 
+    assert(backend->width <= backend->monitor->width_px);
     bar->width = backend->width;
 
     if (pipe(backend->pipe_fds) == -1) {
diff --git a/bar/xcb.c b/bar/xcb.c
index 2a15965..30fdba0 100644
--- a/bar/xcb.c
+++ b/bar/xcb.c
@@ -46,6 +46,14 @@ setup(struct bar *_bar)
     struct private *bar = _bar->private;
     struct xcb_backend *backend = bar->backend.data;
 
+    if (bar->border.left_margin != 0 ||
+        bar->border.right_margin != 0 ||
+        bar->border.top_margin != 0 ||
+        bar->border.bottom_margin)
+    {
+        LOG_WARN("non-zero border margins ignored in X11 backend");
+    }
+
     /* TODO: a lot of this (up to mapping the window) could be done in bar_new() */
     xcb_generic_error_t *e;