diff --git a/cmd/root.go b/cmd/root.go
index eebbfa67..425bded7 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -391,8 +391,18 @@ func unknownSubcommandRunE(cmd *cobra.Command, args []string) error {
 					Message: fmt.Sprintf("unknown flag %s before a subcommand for %q", strings.Join(unknown, ", "), cmd.CommandPath()),
 					Hint:    fmt.Sprintf("flags belong to a subcommand; run `%s --help` to list subcommands and their flags", cmd.CommandPath()),
 					Detail: map[string]any{
+						// Keep the same detail keys as flagDidYouMean's unknown_flag
+						// so a consumer keyed on Type can read a stable shape. The
+						// subcommand isn't resolved here, so suggestions/valid_flags
+						// have no meaningful universe to draw from — emit empty
+						// rather than the group's own (misleading) flags. unknown is
+						// the back-compat singular field; unknown_flags carries the
+						// full list when more than one flag was supplied.
+						"unknown":       strings.Join(unknown, ", "),
 						"unknown_flags": unknown,
 						"command_path":  cmd.CommandPath(),
+						"suggestions":   []string{},
+						"valid_flags":   []string{},
 					},
 				},
 			}
diff --git a/cmd/unknown_subcommand_test.go b/cmd/unknown_subcommand_test.go
index 7f68fdaa..e765341e 100644
--- a/cmd/unknown_subcommand_test.go
+++ b/cmd/unknown_subcommand_test.go
@@ -125,6 +125,31 @@ func TestUnknownSubcommandRunE_FlagBeforeSubcommandIsStructured(t *testing.T) {
 	if !strings.Contains(err.Error(), "unknown flag") {
 		t.Errorf("error = %q, want it to mention an unknown flag", err.Error())
 	}
+
+	// The detail must stay schema-compatible with flagDidYouMean's unknown_flag
+	// (same Type → same keys), so a consumer keyed on Type reads a stable shape.
+	exitErr, ok := err.(*output.ExitError)
+	if !ok || exitErr.Detail == nil {
+		t.Fatalf("expected *output.ExitError with Detail, got %T", err)
+	}
+	if exitErr.Detail.Type != "unknown_flag" {
+		t.Errorf("detail.Type = %q, want unknown_flag", exitErr.Detail.Type)
+	}
+	detail, ok := exitErr.Detail.Detail.(map[string]any)
+	if !ok {
+		t.Fatalf("expected detail to be map[string]any, got %T", exitErr.Detail.Detail)
+	}
+	if detail["unknown"] != "--badflag" {
+		t.Errorf("detail.unknown = %v, want --badflag", detail["unknown"])
+	}
+	if got, _ := detail["unknown_flags"].([]string); len(got) != 1 || got[0] != "--badflag" {
+		t.Errorf("detail.unknown_flags = %v, want [--badflag]", detail["unknown_flags"])
+	}
+	for _, key := range []string{"suggestions", "valid_flags"} {
+		if _, present := detail[key]; !present {
+			t.Errorf("detail.%s missing; must be present (empty) to match the unknown_flag schema", key)
+		}
+	}
 }
 
 func TestUnknownSubcommandRunE_NoArgsShowsHelp(t *testing.T) {