diff --git a/src/Phaseolies/DI/Concerns/EnforcesImmutability.php b/src/Phaseolies/DI/Concerns/EnforcesImmutability.php
index 118e7109..6d572842 100644
--- a/src/Phaseolies/DI/Concerns/EnforcesImmutability.php
+++ b/src/Phaseolies/DI/Concerns/EnforcesImmutability.php
@@ -30,6 +30,10 @@ trait EnforcesImmutability
      */
     public function freeze(): void
     {
+        if ($this->__frozen) {
+            return;
+        }
+
         $reflector = new \ReflectionClass(static::class);
 
         foreach ($reflector->getProperties(\ReflectionProperty::IS_PUBLIC) as $property) {
diff --git a/src/Phaseolies/DI/Container.php b/src/Phaseolies/DI/Container.php
index 9484f57e..b76a967e 100644
--- a/src/Phaseolies/DI/Container.php
+++ b/src/Phaseolies/DI/Container.php
@@ -37,6 +37,13 @@ class Container implements ArrayAccess
      */
     private array $resolving = [];
 
+    /**
+     * Whether each class seen by freezeResolved() is a frozen service.
+     *
+     * @var array<class-string, bool>
+     */
+    private array $immutableClasses = [];
+
     /**
      * The container instance.
      *
@@ -261,7 +268,7 @@ public function get(string $abstract, array $parameters = []): mixed
 
         try {
             if (isset($this->instances[$abstract]) && $this->instances[$abstract] !== null) {
-                return $this->instances[$abstract];
+                return $this->freezeResolved($this->instances[$abstract]);
             }
 
             if (isset($this->bindings[$abstract])) {
@@ -286,7 +293,7 @@ public function get(string $abstract, array $parameters = []): mixed
             // Fallback only: no exact instance and no explicit binding for $abstract.
             foreach ($this->instances as $instance) {
                 if ($instance instanceof $abstract) {
-                    return $instance;
+                    return $this->freezeResolved($instance);
                 }
             }
 
@@ -314,7 +321,7 @@ private function resolveBinding(string $abstract, array $binding, array $paramet
         $concrete = $binding['concrete'];
 
         if (is_callable($concrete)) {
-            return $concrete($this, $parameters);
+            return $this->freezeResolved($concrete($this, $parameters));
         }
 
         if (is_string($concrete) && class_exists($concrete)) {
@@ -376,6 +383,31 @@ public function build(string $concrete, array $parameters = []): object
         return $instance;
     }
 
+    /**
+     * Freeze an object handed out by a closure binding or instance()
+     *
+     * @param mixed $resolved
+     * @return mixed
+     */
+    private function freezeResolved(mixed $resolved): mixed
+    {
+        if (!is_object($resolved)) {
+            return $resolved;
+        }
+
+        $class = $resolved::class;
+
+        $this->immutableClasses[$class] ??= !empty((new \ReflectionClass($resolved))->getAttributes(Immutable::class))
+            && method_exists($resolved, 'freeze')
+            && method_exists($resolved, 'isFrozen');
+
+        if ($this->immutableClasses[$class] && !$resolved->isFrozen()) {
+            $resolved->freeze();
+        }
+
+        return $resolved;
+    }
+
     /**
      * Freeze the instance if the class has the #[Immutable] attribute and uses the EnforcesImmutability trait.
      *
diff --git a/tests/Application/ContainerTest.php b/tests/Application/ContainerTest.php
index 031e29e1..a2563af4 100644
--- a/tests/Application/ContainerTest.php
+++ b/tests/Application/ContainerTest.php
@@ -2896,6 +2896,118 @@ public function testImmutableSingletonBothReferencesAreFrozen()
         $this->assertSame($first, $second);
     }
 
+    // =========================================================================
+    // SERVICES CONFIGURED IN A LAUNCHER (closure bindings and instance())
+    // =========================================================================
+
+    public function testSingletonClosureResultIsFrozenOnFirstResolve()
+    {
+        $payment = new MockPaymentService();
+        $payment->gateway = 'paypal';
+
+        $this->container->singleton(MockPaymentService::class, fn () => $payment);
+
+        $this->assertFalse($payment->isFrozen());
+
+        $resolved = $this->container->get(MockPaymentService::class);
+
+        $this->assertSame($payment, $resolved);
+        $this->assertTrue($resolved->isFrozen());
+        $this->assertSame('paypal', $resolved->gateway);
+    }
+
+    public function testSingletonClosureServiceBlocksMutationAfterResolve()
+    {
+        $payment = new MockPaymentService();
+        $this->container->singleton(MockPaymentService::class, fn () => $payment);
+
+        $resolved = $this->container->get(MockPaymentService::class);
+
+        $this->expectException(ImmutableViolationException::class);
+        $resolved->taxRate = 0.0;
+    }
+
+    public function testLauncherReferenceIsFrozenOnceTheContainerResolvesIt()
+    {
+        $payment = new MockPaymentService();
+        $this->container->singleton(MockPaymentService::class, fn () => $payment);
+        $this->container->get(MockPaymentService::class);
+
+        // The launcher still holds the same object, and it is frozen too.
+        $this->expectException(ImmutableViolationException::class);
+        $payment->gateway = 'late change';
+    }
+
+    public function testInstanceIsFrozenOnFirstResolve()
+    {
+        $payment = new MockPaymentService();
+        $payment->retries = 9;
+
+        $this->container->instance(MockPaymentService::class, $payment);
+
+        $resolved = $this->container->get(MockPaymentService::class);
+
+        $this->assertTrue($resolved->isFrozen());
+        $this->assertSame(9, $resolved->retries);
+    }
+
+    public function testResolvingTwiceKeepsTheConfiguredValues()
+    {
+        $payment = new MockPaymentService();
+        $payment->gateway = 'paypal';
+        $payment->methods = ['wallet'];
+
+        $this->container->singleton(MockPaymentService::class, fn () => $payment);
+
+        $this->container->get(MockPaymentService::class);
+        $again = $this->container->get(MockPaymentService::class);
+
+        $this->assertSame('paypal', $again->gateway);
+        $this->assertSame(['wallet'], $again->methods);
+    }
+
+    public function testMakeWithClosureBindingFreezesEachResult()
+    {
+        $this->container->bind(MockPaymentService::class, fn () => new MockPaymentService());
+
+        $first  = $this->container->make(MockPaymentService::class);
+        $second = $this->container->make(MockPaymentService::class);
+
+        $this->assertNotSame($first, $second);
+        $this->assertTrue($first->isFrozen());
+        $this->assertTrue($second->isFrozen());
+    }
+
+    public function testClosureResultWithoutImmutableAttributeIsNotFrozen()
+    {
+        $this->container->singleton('plain', fn () => new \stdClass());
+
+        $resolved = $this->container->get('plain');
+        $resolved->anything = 'allowed';
+
+        $this->assertSame('allowed', $resolved->anything);
+    }
+
+    public function testClosureReturningNonObjectIsLeftAlone()
+    {
+        $this->container->bind('answer', fn () => 42);
+
+        $this->assertSame(42, $this->container->get('answer'));
+    }
+
+    public function testBuildWithValuesInsteadOfAClosureStillWorks()
+    {
+        $this->container->singleton(
+            MockPaymentService::class,
+            fn ($app) => $app->build(MockPaymentService::class)
+        );
+
+        $resolved = $this->container->get(MockPaymentService::class);
+
+        $this->assertTrue($resolved->isFrozen());
+        $this->assertSame('stripe', $resolved->gateway);
+    }
+
     // =========================================================================
     // TRANSIENT BEHAVIOUR WITH IMMUTABLE
     // =========================================================================