diff --git a/src/output.c b/src/output.c
index c286468..806eb88 100644
--- a/src/output.c
+++ b/src/output.c
@@ -79,6 +79,12 @@ static void frame_handle_buffer(void *data, struct zwlr_screencopy_frame_v1 *fra
 		wl_buffer_destroy(output->frame_buffer);
 	}
 
+	if ((int32_t)width != output->width || (int32_t)height != output->height) {
+		dp_log_fatal("Output/buffer size mismatch: mode=%" PRIi32 "x%" PRIi32 ", buffer=%" PRIu32
+					 "x%" PRIu32,
+				output->width, output->height, width, height);
+	}
+
 	output->frame_format = format;
 	output->frame_stride = (int)stride;
 	output->frame_buffer = dp_buffer_create(output->state, output->width, output->height,
@@ -156,6 +162,10 @@ static void output_handle_geometry(void *data, struct wl_output *wl_output, int3
 
 static void output_handle_mode(void *data, struct wl_output *wl_output, uint32_t flags,
 		int32_t width, int32_t height, int32_t refresh) {
+	if ((flags & WL_OUTPUT_MODE_CURRENT) == 0) {
+		return;
+	}
+
 	struct dp_output *output = data;
 
 	if (output->has_geom) {
@@ -178,6 +188,7 @@ static void output_handle_done(void *data, struct wl_output *wl_output) {
 
 	assert(output->name != NULL);
 
+	assert(output->width > 0 && output->height > 0);
 	if ((output->transform & WL_OUTPUT_TRANSFORM_90) != 0) {
 		output->transformed_width = output->height;
 		output->transformed_height = output->width;