diff --git a/src/CommunityToolkit.Aspire.Hosting.Dapr/DaprDistributedApplicationLifecycleHook.cs b/src/CommunityToolkit.Aspire.Hosting.Dapr/DaprDistributedApplicationLifecycleHook.cs
index 4b3649423..45eb777c4 100644
--- a/src/CommunityToolkit.Aspire.Hosting.Dapr/DaprDistributedApplicationLifecycleHook.cs
+++ b/src/CommunityToolkit.Aspire.Hosting.Dapr/DaprDistributedApplicationLifecycleHook.cs
@@ -11,7 +11,6 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using System.Diagnostics.CodeAnalysis;
-using System.Globalization;
 using System.Net.Sockets;
 using static CommunityToolkit.Aspire.Hosting.Dapr.CommandLineArgs;
 
@@ -240,8 +239,8 @@ private async Task OnBeforeStartAsync(BeforeStartEvent @event, CancellationToken
                         var http = daprCli.GetEndpoint("http");
                         var grpc = daprCli.GetEndpoint("grpc");
 
-                        context.EnvironmentVariables.TryAdd("DAPR_HTTP_PORT", http.Port.ToString(CultureInfo.InvariantCulture));
-                        context.EnvironmentVariables.TryAdd("DAPR_GRPC_PORT", grpc.Port.ToString(CultureInfo.InvariantCulture));
+                        context.EnvironmentVariables.TryAdd("DAPR_HTTP_PORT", http.Property(EndpointProperty.Port));
+                        context.EnvironmentVariables.TryAdd("DAPR_GRPC_PORT", grpc.Property(EndpointProperty.Port));
 
                         context.EnvironmentVariables.TryAdd("DAPR_GRPC_ENDPOINT", grpc);
                         context.EnvironmentVariables.TryAdd("DAPR_HTTP_ENDPOINT", http);
diff --git a/tests/CommunityToolkit.Aspire.Hosting.Azure.Dapr.Tests/DaprAzureContainerAppEnvironmentTests.cs b/tests/CommunityToolkit.Aspire.Hosting.Azure.Dapr.Tests/DaprAzureContainerAppEnvironmentTests.cs
new file mode 100644
index 000000000..a184ee963
--- /dev/null
+++ b/tests/CommunityToolkit.Aspire.Hosting.Azure.Dapr.Tests/DaprAzureContainerAppEnvironmentTests.cs
@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Hosting;
+using Aspire.Hosting.Utils;
+using CommunityToolkit.Aspire.Hosting.Dapr;
+using System.Runtime.CompilerServices;
+
+namespace CommunityToolkit.Aspire.Hosting.Azure.Dapr.Tests;
+
+public class DaprAzureContainerAppEnvironmentTests
+{
+    // End-to-end guard for microsoft/aspire#18242 in the topology that triggers it:
+    // AddAzureContainerAppEnvironment (which contributes the azure-prepare-resources walk) plus a
+    // Dapr sidecar. Invokes the preparer's core operation directly so the test needs no Docker or
+    // provisioning; the non-Azure Dapr.Tests test is the primary deterministic guard.
+    [Fact]
+    public async Task PrepareResourcesWalk_DoesNotThrow_WithAzureEnvironmentAndDaprSidecar()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create();
+
+        // Fake path so the Dapr lifecycle hook does not fail locating the Dapr CLI.
+        builder.AddDapr(o => o.DaprPath = "dapr");
+        builder.AddAzureContainerAppEnvironment("cae");
+
+        var worker = builder.AddContainer("worker", "image")
+            .WithDaprSidecar();
+
+        using var app = builder.Build();
+
+        await ExecuteBeforeStartHooksAsync(app, default);
+
+        var executionContext = new DistributedApplicationExecutionContext(DistributedApplicationOperation.Run);
+
+        var exception = await Record.ExceptionAsync(() =>
+            worker.Resource.GetResourceDependenciesAsync(executionContext, ResourceDependencyDiscoveryMode.DirectOnly));
+
+        Assert.Null(exception);
+    }
+
+    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "ExecuteBeforeStartHooksAsync")]
+    private static extern Task ExecuteBeforeStartHooksAsync(DistributedApplication app, CancellationToken cancellationToken);
+}
diff --git a/tests/CommunityToolkit.Aspire.Hosting.Dapr.Tests/DaprSidecarEndpointAllocationTests.cs b/tests/CommunityToolkit.Aspire.Hosting.Dapr.Tests/DaprSidecarEndpointAllocationTests.cs
new file mode 100644
index 000000000..71b8b2ef7
--- /dev/null
+++ b/tests/CommunityToolkit.Aspire.Hosting.Dapr.Tests/DaprSidecarEndpointAllocationTests.cs
@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Hosting;
+using Aspire.Hosting.Utils;
+using System.Runtime.CompilerServices;
+
+namespace CommunityToolkit.Aspire.Hosting.Dapr.Tests;
+
+public class DaprSidecarEndpointAllocationTests
+{
+    // Regression test for microsoft/aspire#18242: the Dapr env callback must not eagerly read the
+    // sidecar CLI endpoint Port before allocation. GetResourceDependenciesAsync(DirectOnly) is the
+    // operation AzureResourcePreparer runs per compute resource, and reproduces the crash without Azure.
+    [Fact]
+    public async Task AppEnvironmentCallback_DoesNotThrow_WhenDaprSidecarEndpointsNotAllocated()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create();
+
+        // Fake path so the lifecycle hook does not fail locating the Dapr CLI.
+        builder.AddDapr(o => o.DaprPath = "dapr");
+
+        var container = builder.AddContainer("worker", "image")
+            .WithDaprSidecar();
+
+        using var app = builder.Build();
+
+        // Runs the Dapr hook (creates "worker-dapr-cli" and attaches the callback); endpoints stay unallocated.
+        await ExecuteBeforeStartHooksAsync(app, default);
+
+        var executionContext = new DistributedApplicationExecutionContext(DistributedApplicationOperation.Run);
+
+        var dependencies = await container.Resource.GetResourceDependenciesAsync(
+            executionContext,
+            ResourceDependencyDiscoveryMode.DirectOnly);
+
+        Assert.Contains(dependencies, r => r.Name == "worker-dapr-cli");
+
+        // Fire the callback directly (do not resolve - a deferred port blocks until allocation) and
+        // assert the ports are recorded as deferred providers rather than eagerly-read values.
+        var callbackContext = new EnvironmentCallbackContext(executionContext, container.Resource);
+        foreach (var callback in container.Resource.Annotations.OfType<EnvironmentCallbackAnnotation>())
+        {
+            await callback.Callback(callbackContext);
+        }
+
+        Assert.True(callbackContext.EnvironmentVariables.ContainsKey("DAPR_HTTP_PORT"));
+        Assert.True(callbackContext.EnvironmentVariables.ContainsKey("DAPR_GRPC_PORT"));
+        Assert.IsAssignableFrom<IValueProvider>(callbackContext.EnvironmentVariables["DAPR_HTTP_PORT"]);
+        Assert.IsAssignableFrom<IValueProvider>(callbackContext.EnvironmentVariables["DAPR_GRPC_PORT"]);
+    }
+
+    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "ExecuteBeforeStartHooksAsync")]
+    private static extern Task ExecuteBeforeStartHooksAsync(DistributedApplication app, CancellationToken cancellationToken);
+}