diff --git a/tests/unit/test_ffi_context.nim b/tests/unit/test_ffi_context.nim
index 52c435f..09304e9 100644
--- a/tests/unit/test_ffi_context.nim
+++ b/tests/unit/test_ffi_context.nim
@@ -27,6 +27,12 @@ proc deinitCallbackData(d: var CallbackData) =
 proc testCallback(
     retCode: cint, msg: ptr cchar, len: csize_t, userData: pointer
 ) {.cdecl, gcsafe, raises: [].} =
+  # RET_STALE_WARN is a progress ping, not an answer: a slow handler (or a slow
+  # CI runner) trips it before the terminal code arrives.  Waking `waitCallback`
+  # here would hand the test a non-terminal retCode and let it tear the context
+  # down mid-flight.  Tests that assert on the pings use `staleCallback`.
+  if retCode == RET_STALE_WARN:
+    return
   let d = cast[ptr CallbackData](userData)
   acquire(d[].lock)
   d[].retCode = retCode