diff --git a/include/wlr/render/swapchain.h b/include/wlr/render/swapchain.h
index 4ca1ac590..e09158aae 100644
--- a/include/wlr/render/swapchain.h
+++ b/include/wlr/render/swapchain.h
@@ -46,5 +46,9 @@ struct wlr_buffer *wlr_swapchain_acquire(struct wlr_swapchain *swapchain);
  */
 bool wlr_swapchain_has_buffer(struct wlr_swapchain *swapchain,
 	struct wlr_buffer *buffer);
+/**
+ * Count how many free slots there are left in the swapchain.
+ */
+int wlr_swapchain_count_free_slots(const struct wlr_swapchain *swapchain);
 
 #endif
diff --git a/render/swapchain.c b/render/swapchain.c
index 24d6f1a87..f42507ddf 100644
--- a/render/swapchain.c
+++ b/render/swapchain.c
@@ -120,3 +120,12 @@ bool wlr_swapchain_has_buffer(struct wlr_swapchain *swapchain,
 	}
 	return false;
 }
+
+int wlr_swapchain_count_free_slots(const struct wlr_swapchain *swapchain)
+{
+	int count = 0;
+	for (size_t i = 0; i < WLR_SWAPCHAIN_CAP; i++) {
+		count += !swapchain->slots[i].acquired;
+	}
+	return count;
+}