diff --git a/CHANGELOG.md b/CHANGELOG.md
index 86cfc55..7dec971 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,6 +32,8 @@ APIs change between minors without a deprecation period.
 - **`llmgw mirror add-peer` on a mirror with a machine of its own.** It set the second mirror up and then
   failed for want of the control plane's server.yaml; now it prints the `llmgw ctl config set mirror.peers`
   to run on a control plane.
+- **Models fetched before checksums were kept reach the second mirror.** A mirror kept in step copies only what it
+  can check, and those files had no sha256; a mirror with peers now works theirs out and records them, once.
 
 ## v0.15.2 — 2026-10-29
 
diff --git a/internal/mirror/peer.go b/internal/mirror/peer.go
index 53254ce..deeeac4 100644
--- a/internal/mirror/peer.go
+++ b/internal/mirror/peer.go
@@ -3,6 +3,7 @@ package mirror
 import (
 	"context"
 	"log/slog"
+	"path/filepath"
 	"strings"
 	"time"
 )
@@ -24,6 +25,13 @@ type Peers struct {
 
 // Run reads the peers until ctx ends.
 func (p *Peers) Run(ctx context.Context) {
+	// Files fetched before checksums were kept have none, and a peer copies
+	// only what it can check: they are given theirs, beside the sync.
+	go func() {
+		if n := p.M.FillChecksums(ctx); n > 0 {
+			p.Log.Info("recorded the checksums of files that had none, so peer mirrors can copy them", "files", n)
+		}
+	}()
 	t := time.NewTicker(PeerInterval)
 	defer t.Stop()
 	for {
@@ -122,3 +130,33 @@ func (p *Peers) SyncOnce(ctx context.Context, c *Client) {
 		}
 	}
 }
+
+// FillChecksums records the sha256 of every file the mirror holds without
+// one, and says how many it recorded.
+func (m *Manager) FillChecksums(ctx context.Context) int {
+	entries, err := List(m.root)
+	if err != nil {
+		return 0
+	}
+	n := 0
+	for _, e := range entries {
+		if ctx.Err() != nil {
+			break
+		}
+		path := filepath.Join(m.root, e.Model, e.Version, e.File)
+		if readChecksum(path) != "" || m.isRunning(e.Model, e.Version, e.File) {
+			continue
+		}
+		sum, err := sha256File(path)
+		if err != nil {
+			m.log.Warn("could not read a file's checksum", "file", path, "err", err)
+			continue
+		}
+		if err := writeChecksum(path, sum); err != nil {
+			m.log.Warn("could not record a file's checksum", "file", path, "err", err)
+			continue
+		}
+		n++
+	}
+	return n
+}
diff --git a/internal/mirror/peer_test.go b/internal/mirror/peer_test.go
index 6ff5e29..cff3550 100644
--- a/internal/mirror/peer_test.go
+++ b/internal/mirror/peer_test.go
@@ -172,3 +172,29 @@ func TestAModelsAddressIsMovedToAMirrorThatAnswers(t *testing.T) {
 		t.Errorf("none up: %s", got)
 	}
 }
+
+// A file fetched before checksums were kept is given one, and is then copied.
+func TestAFileWithoutAChecksumIsGivenOneAndThenCopied(t *testing.T) {
+	a, b := newTestMirror(t), newTestMirror(t)
+	path := filepath.Join(a.root, "old", "v1", "m.gguf")
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte("fetched long ago"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	pb := &Peers{M: b.m, Log: discardLog()}
+	pb.SyncOnce(t.Context(), a.client(t))
+	time.Sleep(100 * time.Millisecond)
+	if b.has("old", "v1") {
+		t.Fatal("copied without a checksum to check it by")
+	}
+	if n := a.m.FillChecksums(t.Context()); n != 1 || readChecksum(path) == "" {
+		t.Fatalf("recorded %d", n)
+	}
+	if a.m.FillChecksums(t.Context()) != 0 {
+		t.Error("recorded again")
+	}
+	pb.SyncOnce(t.Context(), a.client(t))
+	waitPresent(t, b, "old", "v1")
+}