diff --git a/mcphttp/cache_test.go b/mcphttp/cache_test.go
index 7191cc52b891715b6d70163c2aa8c7f3f9623429..3956cef30172953c381cd8ea24ac61f0493013d7 100644
--- a/mcphttp/cache_test.go
+++ b/mcphttp/cache_test.go
@@ -88,6 +88,44 @@ 	assert.Equal(t, []string{wantVary}, rec.Header().Values("Vary"))
 	assert.Equal(t, "ab", rec.Body.String())
 }
 
+// TestAFlushBeforeAnyWriteStillCarriesTheHeaders is what the Flush method earns.
+//
+// A handler that flushes before writing anything commits the response through
+// the flush, not through Write — so the Write hook never runs, and without a
+// Flush of its own the wrapper is bypassed entirely and the response leaves with
+// no Cache-Control and no Vary. Every other test here writes first, which sets
+// the headers on the way in and leaves the flush path unmeasured: deleting Flush
+// kept all of them green.
+//
+// It has to run against a real server. httptest.ResponseRecorder's Header()
+// hands back the live map, so a recorder reports the headers as set no matter
+// when — or whether — the wrapper committed them, and reports a pass for exactly
+// this bug.
+func TestAFlushBeforeAnyWriteStillCarriesTheHeaders(t *testing.T) {
+	release := make(chan struct{})
+	srv := httptest.NewServer(mcphttp.PrivateCache(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "text/event-stream")
+			if err := http.NewResponseController(w).Flush(); err != nil {
+				t.Errorf("flush: %v", err)
+			}
+			<-release
+			_, _ = w.Write([]byte(": keepalive\n\n"))
+		})))
+	t.Cleanup(func() {
+		close(release)
+		srv.Close()
+	})
+
+	resp, err := (&http.Client{Timeout: 5 * time.Second}).Get(srv.URL)
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = resp.Body.Close() })
+
+	assert.Equal(t, wantCacheControl, resp.Header.Get("Cache-Control"),
+		"the response committed through Flush, so only Flush could have set this")
+	assert.Equal(t, wantVary, resp.Header.Get("Vary"))
+}
+
 // TestFlushOnTheWrapperStreams covers the flush path, which cacheWriter answers
 // itself rather than delegating.
 //