diff --git a/collects/ffi/unsafe/com.rkt b/collects/ffi/unsafe/com.rkt
index 6437e152ea..5deec7e37a 100644
--- a/collects/ffi/unsafe/com.rkt
+++ b/collects/ffi/unsafe/com.rkt
@@ -1137,6 +1137,7 @@
    [(real? arg) 'double]
    [(com-object? arg) 'com-object]
    [(IUnknown? arg) 'iunknown]
+   [(eq? com-omit arg) 'any]
    [else (error 'com "cannot infer marshal format for value: ~e" arg)]))
 
 (define (elem-desc-ref func-desc i)