diff --git a/internal/catalogue/declaration.go b/internal/catalogue/declaration.go
index afd1087..a592599 100644
--- a/internal/catalogue/declaration.go
+++ b/internal/catalogue/declaration.go
@@ -1685,7 +1685,10 @@ func prepared(from map[string]any) map[string]any {
 	for k, v := range from {
 		step[k] = v
 	}
-	step["id"] = fmt.Sprint(from["id"]) + ".prepare"
+	// **A hyphen, not a dot.** A resource's id is `<module>.<its own id>`, and a module's name may
+	// itself contain a dot (`novox.be`), so the module is everything before the *last* dot — which
+	// only works if what the mesh derives adds no dot of its own.
+	step["id"] = fmt.Sprint(from["id"]) + "-prepare"
 	step["name"] = fmt.Sprint(from["name"]) + "-prepare"
 	step["run-once"] = true
 	step["args"] = []any{PreparationArgument}
diff --git a/internal/catalogue/prepares_test.go b/internal/catalogue/prepares_test.go
index dd414c8..eaae43b 100644
--- a/internal/catalogue/prepares_test.go
+++ b/internal/catalogue/prepares_test.go
@@ -3,6 +3,7 @@ package catalogue
 import (
 	"encoding/json"
 	"fmt"
+	"strings"
 	"testing"
 )
 
@@ -57,13 +58,18 @@ func TestThePreparationRunsTheModulesOwnCodeAndComesRightBeforeIt(t *testing.T)
 	ids := idsOf(out)
 	at := -1
 	for i, id := range ids {
-		if id == "gitea.runtime.prepare" {
+		if id == "gitea.runtime-prepare" {
 			at = i
 		}
 	}
 	if at < 0 {
 		t.Fatalf("nothing prepares this module's state: %v", ids)
 	}
+	// A module's name may contain a dot, so a resource's module is everything before the last one —
+	// which the derived id must not add to, or a machine reads the wrong owner from it.
+	if strings.Count("gitea.runtime-prepare", ".") != 1 {
+		t.Fatal("the derived id adds a dot, so what owns it cannot be read from it")
+	}
 	if ids[at+1] != "gitea.runtime" {
 		t.Fatalf("the preparation is not immediately before the module's own code: %v", ids)
 	}
@@ -79,7 +85,7 @@ func TestThePreparationRunsTheModulesOwnCodeAndComesRightBeforeIt(t *testing.T)
 func TestThePreparationIsGivenWhatTheModuleIsGiven(t *testing.T) {
 	out := declaredFor(t, aPreparingModule())
 	declared := byID(out)
-	step, workload := declared["gitea.runtime.prepare"], declared["gitea.runtime"]
+	step, workload := declared["gitea.runtime-prepare"], declared["gitea.runtime"]
 	if step == nil || workload == nil {
 		t.Fatalf("expected both, got %v", idsOf(out))
 	}
@@ -108,7 +114,7 @@ func TestAModuleThatPreparesNothingGetsNoStep(t *testing.T) {
 	m := aPreparingModule()
 	m.Prepares = false
 	for _, id := range idsOf(declaredFor(t, m)) {
-		if id == "gitea.runtime.prepare" {
+		if id == "gitea.runtime-prepare" {
 			t.Fatal("a module that prepares nothing was given a preparation")
 		}
 	}