diff --git a/modules/mesh-delivery/cmd/mesh-delivery/holder.go b/modules/mesh-delivery/cmd/mesh-delivery/holder.go
index 7b448e2b..6a69eb1d 100644
--- a/modules/mesh-delivery/cmd/mesh-delivery/holder.go
+++ b/modules/mesh-delivery/cmd/mesh-delivery/holder.go
@@ -542,6 +542,9 @@ func (h *Holder) PullMerged(p PullEvent) {
 			}
 		}
 	}
+	if d != nil && d.MergedAs != "" && sameCommit(d.MergedAs, p.MergeCommit) {
+		return // this merge is already taken: heard again, past the bus's de-duplication window, it changes nothing
+	}
 	now := h.Now()
 	var ts []Transition
 	if over := startedOverFor(d, p.Number); over != "" {
diff --git a/modules/mesh-delivery/cmd/mesh-delivery/pullkey.go b/modules/mesh-delivery/cmd/mesh-delivery/pullkey.go
index 2447b91b..9086de56 100644
--- a/modules/mesh-delivery/cmd/mesh-delivery/pullkey.go
+++ b/modules/mesh-delivery/cmd/mesh-delivery/pullkey.go
@@ -56,7 +56,7 @@ func (h *Holder) KeepPull(p PullEvent) {
 
 // KeepVerdict writes a verdict into the key of its pull request, when the key holds that head and trunk commit.
 func (h *Holder) KeepVerdict(c CheckedEvent) {
-	if h.Pulls == nil || c.Group != "" || c.Number == 0 || c.Commit == "" {
+	if h.Pulls == nil || c.Group != "" || c.Number == 0 || c.Commit == "" || c.Trunk == "" {
 		return
 	}
 	verdict := c.Verdict
@@ -64,7 +64,7 @@ func (h *Holder) KeepVerdict(c CheckedEvent) {
 		return
 	}
 	err := h.Pulls.Change(pullKeyName(c.Owner, c.Repo, c.Number), func(k PullKey) (PullKey, bool) {
-		if !sameCommit(k.Head, c.Commit) || (c.Trunk != "" && !sameCommit(k.Trunk, c.Trunk)) || k.Verdict == verdict {
+		if !sameCommit(k.Head, c.Commit) || !sameCommit(k.Trunk, c.Trunk) || k.Verdict == verdict {
 			return k, false
 		}
 		k.Verdict = verdict
diff --git a/modules/mesh-delivery/cmd/mesh-delivery/pullkey_test.go b/modules/mesh-delivery/cmd/mesh-delivery/pullkey_test.go
index 936c4e4f..37e951df 100644
--- a/modules/mesh-delivery/cmd/mesh-delivery/pullkey_test.go
+++ b/modules/mesh-delivery/cmd/mesh-delivery/pullkey_test.go
@@ -138,3 +138,34 @@ func TestAPullRequestMarkedReadyHasItsCheckAskedOnTheReadyStream(t *testing.T) {
 		t.Fatalf("the check of an unmarked pull request was asked with ready %v", w2.ctl.checkReady)
 	}
 }
+
+func TestATrunkLessVerdictWritesNothingToTheKey(t *testing.T) {
+	w := newWorld(t)
+	pulls := newFakePulls()
+	w.h.Pulls = pulls
+	w.h.KeepPull(announcedAt(readyHead, "t1t1t1t1t1t1"))
+	w.h.KeepVerdict(judgedAt("novox/app", 7, readyHead, "pass", ""))
+	if got := pulls.get(appKey); got.Verdict != "" {
+		t.Fatalf("a verdict naming no trunk commit was written: %+v", got)
+	}
+}
+
+// The forge's catch-up after a restart can announce a merge again past the bus's de-duplication window (issue 975):
+// heard again, it changes nothing, and moves no trunk back.
+func TestTheSameMergeHeardAgainAfterALaterMergeMovesNoTrunkBack(t *testing.T) {
+	w := newWorld(t)
+	a, b := "aaaaaaaaaaaaaaaa", "bbbbbbbbbbbbbbbb"
+	w.h.PullUpdated(pr("novox/app", 7, readyHead, "feat/x", "src/a.go"))
+	w.h.PullUpdated(pr("novox/app", 8, a, "feat/y", "src/a.go"))
+	w.h.PullUpdated(pr("novox/app", 9, b, "feat/z", "src/a.go"))
+	w.h.Checked(judgedAt("novox/app", 7, readyHead, "pass", "m8m8m8m8m8m8"))
+	w.h.PullMerged(merged("novox/app", 8, a, "m8m8m8m8m8m8"))
+	w.h.PullMerged(merged("novox/app", 9, b, "m9m9m9m9m9m9"))
+	id := IDOf("novox/app", readyHead)
+	before := w.delivery(id)
+	w.h.PullMerged(merged("novox/app", 8, a, "m8m8m8m8m8m8")) // announced again, past the window
+	after := w.delivery(id)
+	if after.TrunkNow != before.TrunkNow || after.TrunkNow != "m9m9m9m9m9m9" {
+		t.Fatalf("the trunk moved from %q to %q on a merge heard again; wanted it to stay m9m9m9m9m9m9", before.TrunkNow, after.TrunkNow)
+	}
+}