diff --git a/modules/mesh-delivery-checker/internal/check/engines.go b/modules/mesh-delivery-checker/internal/check/engines.go
index 2e077789..7b7f1909 100644
--- a/modules/mesh-delivery-checker/internal/check/engines.go
+++ b/modules/mesh-delivery-checker/internal/check/engines.go
@@ -214,7 +214,13 @@ func (e EngineCompositions) inSandbox(ctx context.Context, c *Case, head, node s
 			delete(verdicts, name) // a manifest the change brings is the checker's own judge's (ADR 0578 §2)
 		}
 	}
-	req := composer.Request{V: composer.Version, Input: a.Input, Depth: composer.DepthCompose, Machines: []string{node},
+	// The answer carries its input as the object the seat's contract names, decoded with its numbers as written
+	// (json.Number), so encoding it again gives the composer the same values the engine sent.
+	input, err := json.Marshal(a.Input)
+	if err != nil {
+		return a, fmt.Errorf("the engine of %s answered a composition input that cannot be encoded again: %w", node, err)
+	}
+	req := composer.Request{V: composer.Version, Input: input, Depth: composer.DepthCompose, Machines: []string{node},
 		Cases: []composer.Case{{Name: "change", Manifests: manifests, Verdicts: verdicts}}}
 	raw, err := json.Marshal(req)
 	if err != nil {
diff --git a/modules/mesh-delivery-checker/internal/check/engines_test.go b/modules/mesh-delivery-checker/internal/check/engines_test.go
index fed2774f..18f5ac10 100644
--- a/modules/mesh-delivery-checker/internal/check/engines_test.go
+++ b/modules/mesh-delivery-checker/internal/check/engines_test.go
@@ -143,7 +143,7 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 		}
 		host := CaseOf(c, map[string]string{repoA: trunkA, nodeEngineRepo: trunkA})
 		withInput := composed("anchor")
-		withInput.Input = json.RawMessage(`{"nodes":[{"name":"anchor"}]}`)
+		withInput.Input = map[string]any{"nodes": []any{map[string]any{"name": "anchor"}}}
 		e := &fakeEngines{answers: map[string]delivery.ComposeCandidateAnswer{"anchor": withInput}}
 		sb := &fakeSandbox{v: func(node string) composer.Verdict {
 			return composer.Verdict{V: composer.Version, Cases: []composer.CaseVerdict{{Name: "change",
@@ -162,7 +162,7 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 		var req composer.Request
 		_ = json.Unmarshal(job.Request, &req)
 		if job.Fetch["repository"] != nodeEngineRepo || job.Fetch["commit"] != head2 || job.Package != composer.Package ||
-			string(req.Input) != string(withInput.Input) || req.Cases[0].Manifests["web"].Digest == "" {
+			string(req.Input) != `{"nodes":[{"name":"anchor"}]}` || req.Cases[0].Manifests["web"].Digest == "" {
 			t.Errorf("job = %+v, request %+v", job, req)
 		}
 		if v.State != delivery.CompositionFail || v.SDK != head2 || !strings.Contains(v.Words, "the new composer refuses it") {