diff --git a/client/internal/certproof/helper_run_test.go b/client/internal/certproof/helper_run_test.go
index 8a893f903..b3c07cfcd 100644
--- a/client/internal/certproof/helper_run_test.go
+++ b/client/internal/certproof/helper_run_test.go
@@ -3,6 +3,7 @@
 package certproof
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"os/exec"
@@ -89,6 +90,32 @@ func TestRunHelperCmd_ReturnsWhenAGrandchildHoldsTheOutputPipe(t *testing.T) {
 	}
 }
 
+func TestRunHelperCmd_ReturnsWhenTheDeadlineKillsTheLauncher(t *testing.T) {
+	req := HelperRequest{Challenges: []HelperChallenge{{Nonce: []byte("asked")}}}
+
+	// The shape the daemon actually meets on macOS: the process it launches is only a
+	// launcher, the work happens in a grandchild, and the deadline reaps the launcher
+	// while the grandchild keeps the stdout it inherited open. Unlike the case above
+	// the process is killed, so Wait reports that rather than ErrWaitDelay.
+	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
+	defer cancel()
+	cmd := exec.CommandContext(ctx, "/bin/sh", "-c", "cat >/dev/null; sleep 10 & sleep 10")
+
+	done := make(chan error, 1)
+	go func() {
+		proofs, err := runHelperCmd(cmd, req)
+		assert.Empty(t, proofs, "a run the deadline cut short has nothing trustworthy to report")
+		done <- err
+	}()
+
+	select {
+	case err := <-done:
+		require.Error(t, err, "the run was cut short, so it must not be reported as a success")
+	case <-time.After(5 * time.Second):
+		t.Fatal("runHelperCmd never returned after the deadline killed the launcher, so the collector's busy latch would stay set for the life of the daemon")
+	}
+}
+
 func TestRunHelperCmd_RejectsGarbage(t *testing.T) {
 	req := HelperRequest{Challenges: []HelperChallenge{{Nonce: []byte("asked")}}}