diff --git a/modules/mesh-delivery/cmd/mesh-delivery/ready.go b/modules/mesh-delivery/cmd/mesh-delivery/ready.go
index f6f98672..fa36708a 100644
--- a/modules/mesh-delivery/cmd/mesh-delivery/ready.go
+++ b/modules/mesh-delivery/cmd/mesh-delivery/ready.go
@@ -69,8 +69,14 @@ type ReadyRun struct {
 	Merged *time.Time `json:"merged,omitempty"`
 	// Failed is why it is not merged and will not be on this head: its check failed. Said once on the pull request.
 	Failed string `json:"failed,omitempty"`
+	// OtherBase is the branch its pull request merges into when that is not main: never merged here, said once on the
+	// pull request (novox/hq ADR 0398 §4, issue 948).
+	OtherBase string `json:"other_base,omitempty"`
 }
 
+// MergeBranch is the one branch this owner merges into (novox/hq ADR 0398 §4): a merge into any other is its author's.
+const MergeBranch = "main"
+
 // mergedBy is who a merge this owner made on a ready mark is said to be by, in its transitions.
 func (r *ReadyRun) mergedBy() string {
 	if r == nil || r.Merged == nil {
@@ -185,6 +191,18 @@ func (h *Holder) readyAsks(now time.Time) []func() {
 			}
 			continue
 		}
+		if p.Base != MergeBranch {
+			if r.OtherBase != p.Base {
+				r.OtherBase = p.Base
+				h.Logf("[mesh-delivery] %s is marked ready and not merged: it merges into %s, not %s", d.ID, p.Base, MergeBranch)
+				h.keep(d)
+				asks = append(asks, h.sayOn(d, fmt.Sprintf("mesh-delivery: **not merged.** This pull request is marked ready "+
+					"at %s, and it merges into %s. Only a merge into %s is this owner's; a merge into another branch is its "+
+					"author's (novox/hq ADR 0398 §4). The mark stays.", mark.Head, p.Base, MergeBranch)))
+			}
+			continue
+		}
+		r.OtherBase = ""
 		r.Failed = ""
 		waits := h.readyWaits(d)
 		if waits != r.Waits {
diff --git a/modules/mesh-delivery/cmd/mesh-delivery/ready_test.go b/modules/mesh-delivery/cmd/mesh-delivery/ready_test.go
index e818e9b1..565f08bb 100644
--- a/modules/mesh-delivery/cmd/mesh-delivery/ready_test.go
+++ b/modules/mesh-delivery/cmd/mesh-delivery/ready_test.go
@@ -197,3 +197,31 @@ func TestAGroupMergesItsMarkedMembersInOrderOnlyOnceComposed(t *testing.T) {
 		t.Fatalf("after the first member merged, the next was not: %v", w.forge.merges)
 	}
 }
+
+// **A merge into another branch than main is its author's** (novox/hq ADR 0398 §4, issue 948): a ready mark on a pull
+// request whose base is not main is never merged by this owner; it says so once on the pull request and leaves the mark.
+func TestAMarkedGreenPullRequestIntoAnotherBranchIsNotMergedAndSaidOnce(t *testing.T) {
+	w := newWorld(t)
+	p := pr("novox/app", 7, readyHead, "feat/x", "src/a.go")
+	p.Base = "release/x"
+	w.h.PullUpdated(p)
+	w.h.Checked(judgedAt("novox/app", 7, readyHead, "pass", "t1t1t1t1t1t1"))
+	open := markedPull("novox/app", 7, readyHead, readyHead)
+	open.Base = "release/x"
+	w.forge.open = []OpenPull{open}
+	for range 3 {
+		w.h.SeeOpenPulls()
+		w.settleAll()
+		w.later(2 * time.Minute)
+	}
+	if len(w.forge.merges) != 0 {
+		t.Fatalf("a pull request into release/x was merged: %v", w.forge.merges)
+	}
+	if len(w.forge.comments) != 1 || !strings.Contains(w.forge.comments[0], "another branch") ||
+		!strings.Contains(w.forge.comments[0], "0398") {
+		t.Fatalf("not said exactly once on the pull request: %v", w.forge.comments)
+	}
+	if len(w.forge.unlabels) != 0 {
+		t.Fatalf("the mark was taken off: %v", w.forge.unlabels)
+	}
+}