diff --git a/demos/gears.c b/demos/gears.c
index f7b8cada..72916dc7 100644
--- a/demos/gears.c
+++ b/demos/gears.c
@@ -218,7 +218,8 @@ static void cxg_wait_for_previous_frame(struct cx_gears *cxg)
 
     if (ID3D12Fence_GetCompletedValue(fence->fence) < v)
     {
-        ID3D12Fence_SetEventOnCompletion(fence->fence, v, fence->event);
+        hr = ID3D12Fence_SetEventOnCompletion(fence->fence, v, fence->event);
+        assert(SUCCEEDED(hr));
         demo_wait_event(fence->event, INFINITE);
     }
 
diff --git a/demos/triangle.c b/demos/triangle.c
index 15f348f6..96ad8379 100644
--- a/demos/triangle.c
+++ b/demos/triangle.c
@@ -142,7 +142,8 @@ static void cxt_wait_for_previous_frame(struct cx_triangle *cxt)
 
     if (ID3D12Fence_GetCompletedValue(fence->fence) < v)
     {
-        ID3D12Fence_SetEventOnCompletion(fence->fence, v, fence->event);
+        hr = ID3D12Fence_SetEventOnCompletion(fence->fence, v, fence->event);
+        assert(SUCCEEDED(hr));
         demo_wait_event(fence->event, INFINITE);
     }