diff --git a/CHANGELOG.md b/CHANGELOG.md
index 06bea82..6d2d59a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+- Handle optional route parameters with constraints (#222)
+
 ### Changed
 
 - Bump System.Reflection.MetadataLoadContext from 10.0.8 to 10.0.9 (#221)
diff --git a/TypeContractor.Tests/Helpers/ApiHelpersTests.cs b/TypeContractor.Tests/Helpers/ApiHelpersTests.cs
index b0cae8f..418e356 100644
--- a/TypeContractor.Tests/Helpers/ApiHelpersTests.cs
+++ b/TypeContractor.Tests/Helpers/ApiHelpersTests.cs
@@ -73,6 +73,27 @@ public void BuildApiEndpoint_Skips_Ignored_Methods()
 		endpoint.Should().BeEmpty();
 	}
 
+	[Fact]
+	public void BuildApiEndpoint_Handles_Optional_Route_Part()
+	{
+		// Arrange
+		var endpointMethod = typeof(RouteController).GetMethod(nameof(RouteController.DeleteWithOptionalPart), [typeof(Guid), typeof(Guid), typeof(Guid), typeof(Guid), typeof(Guid?), typeof(CancellationToken)])!;
+
+		// Act
+		var endpoints = ApiHelpers.BuildApiEndpoint(endpointMethod);
+
+		// Assert
+		endpoints.Should().ContainSingle();
+		var endpoint = endpoints.First();
+
+		endpoint.Route.Should().Be("deletemember/{id}/{referenceId}/{certificationGroupId?}");
+		endpoint.Parameters.Should()
+			.HaveCount(3)
+			.And.Contain(x => x.FromRoute && x.Name == "id" && !x.IsOptional)
+			.And.Contain(x => x.FromRoute && x.Name == "referenceId" && !x.IsOptional)
+			.And.Contain(x => x.FromRoute && x.Name == "certificationGroupId" && x.IsOptional);
+	}
+
 	[TypeContractorIgnore]
 	internal class IgnoredController : ControllerBase { }
 
@@ -93,4 +114,10 @@ internal class LegacyController : ControllerBase
 
 	[TypeContractorName("RenamedApi")]
 	internal class RenamedSuffixController : ControllerBase { }
+
+	internal class RouteController : ControllerBase
+	{
+		[HttpDelete("deletemember/{id:Guid}/{referenceId:Guid}/{certificationGroupId:Guid?}")]
+		public ActionResult DeleteWithOptionalPart([FromHeader] Guid organizationId, [FromHeader] Guid customerId, Guid id, Guid referenceId, Guid? certificationGroupId, CancellationToken cancellationToken) => NotFound();
+	}
 }
diff --git a/TypeContractor.Tests/TypeScript/ApiClientWriterTests.cs b/TypeContractor.Tests/TypeScript/ApiClientWriterTests.cs
index c2067d0..4b5ac97 100644
--- a/TypeContractor.Tests/TypeScript/ApiClientWriterTests.cs
+++ b/TypeContractor.Tests/TypeScript/ApiClientWriterTests.cs
@@ -359,6 +359,35 @@ public void Handles_Optional_Route_Parameter()
 			.And.NotContain("url.searchParams.append(");
 	}
 
+	[Fact]
+	public void Handles_Nullable_Route_Parameter()
+	{
+		// Arrange
+		var apiClient = new ApiClient("TestClient", "TestController", "test", null);
+		apiClient.AddEndpoint(new ApiClientEndpoint("getLatest", "latest/{id}/{referenceId}/{groupId?}", EndpointMethod.GET, null, typeof(Guid), false, [
+			new EndpointParameter("id", typeof(Guid), null, false, false, true, false, false, false, false, false),
+			new EndpointParameter("referenceId", typeof(Guid), null, false, false, true, false, false, false, false, false),
+			new EndpointParameter("groupId", typeof(Guid?), typeof(Guid), false, false, true, false, false, false, false, true),
+		], null));
+
+		// Act
+		var result = Sut.Write(apiClient, [], _converter, true, _templateFn, Casing.Pascal);
+
+		// Assert
+		var file = File.ReadAllText(result).Trim();
+		file.Should()
+			.NotBeEmpty()
+			.And.Contain("import { z } from 'zod';")
+			.And.Contain("export class TestClient {")
+			.And.Contain("public async getLatest(id: string, referenceId: string, groupId: string | undefined, cancellationToken: AbortSignal = null): Promise<string> {")
+			.And.Contain("const url = new URL(`test/latest/${id}/${referenceId}/{groupId?}`, window.location.origin);")
+			.And.Contain("if (groupId != undefined)")
+			.And.Contain("url.pathname = url.pathname.replace('{groupId?}', groupId.toString());")
+			.And.Contain("else")
+			.And.Contain("url.pathname = url.pathname.replace('/{groupId?}', '');")
+			.And.NotContain("url.searchParams.append(");
+	}
+
 	[Theory]
 	[InlineData(Casing.Camel)]
 	[InlineData(Casing.Pascal)]
diff --git a/TypeContractor/Helpers/ApiHelpers.cs b/TypeContractor/Helpers/ApiHelpers.cs
index 0b95e04..764dad3 100644
--- a/TypeContractor/Helpers/ApiHelpers.cs
+++ b/TypeContractor/Helpers/ApiHelpers.cs
@@ -12,7 +12,7 @@ public static partial class ApiHelpers
 {
 	private static readonly Regex _routeParameterRegex = RouteParameterRegexImpl();
 
-	[GeneratedRegex("{([A-Za-z]+)(:[[A-Za-z]+)?}")]
+	[GeneratedRegex("{([A-Za-z]+)(:[[A-Za-z?]+)?}")]
 	private static partial Regex RouteParameterRegexImpl();
 
 	public static ApiClient? BuildApiClient(Type controller, List<MethodInfo> endpoints)
@@ -121,7 +121,8 @@ private static (string Route, EndpointMethod HttpMethod) DetermineRoute(MethodIn
 		{
 			if (!match.Success) continue;
 			if (match.Groups.Count < 3) continue;
-			finalRoute = finalRoute.Replace(match.Value, $"{{{match.Groups[1].Value}}}");
+			var optional = match.Groups[2].Value.EndsWith('?') ? "?" : "";
+			finalRoute = finalRoute.Replace(match.Value, $"{{{match.Groups[1].Value}{optional}}}");
 		}
 
 		var httpMethod = method.AttributeType.Name switch
@@ -152,7 +153,13 @@ private static bool ParameterIsOptional(ParameterInfo parameterInfo, string fina
 		if (!ParameterIsFromRoute(parameterInfo, finalRoute))
 			return false;
 
-		return finalRoute.Contains($"{{{parameterInfo.Name}?}}");
+		if (finalRoute.Contains($"{{{parameterInfo.Name}?}}"))
+			return true;
+
+		if (IsNullable(parameterInfo.ParameterType))
+			return true;
+
+		return false;
 	}
 
 	private static bool ParameterIsFromQuery(ParameterInfo parameterInfo, EndpointMethod httpMethod, string finalRoute)