diff --git a/.chronus/changes/multipart-fix-2024-7-19-14-19-40.md b/.chronus/changes/multipart-fix-2024-7-19-14-19-40.md
new file mode 100644
index 0000000000..335fae7d55
--- /dev/null
+++ b/.chronus/changes/multipart-fix-2024-7-19-14-19-40.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+Fix multipart for client customization
\ No newline at end of file
diff --git a/packages/typespec-client-generator-core/src/types.ts b/packages/typespec-client-generator-core/src/types.ts
index dddcae2b00..be899c5f11 100644
--- a/packages/typespec-client-generator-core/src/types.ts
+++ b/packages/typespec-client-generator-core/src/types.ts
@@ -1795,18 +1795,6 @@ export function getAllModelsWithDiagnostics(
         ogs.push(...operationGroup.subOperationGroups);
       }
     }
-    // orphan models
-    for (const model of client.service.models.values()) {
-      handleServiceOrphanType(context, model);
-    }
-    // orphan enums
-    for (const enumType of client.service.enums.values()) {
-      handleServiceOrphanType(context, enumType);
-    }
-    // orphan unions
-    for (const unionType of client.service.unions.values()) {
-      handleServiceOrphanType(context, unionType);
-    }
     // server parameters
     const servers = getServers(context.program, client.service);
     if (servers !== undefined && servers[0].parameters !== undefined) {
@@ -1826,6 +1814,21 @@ export function getAllModelsWithDiagnostics(
       updateUsageOfModel(context, UsageFlags.ApiVersionEnum, sdkVersionsEnum);
     }
   }
+  // update for orphan models/enums/unions
+  for (const client of listClients(context)) {
+    // orphan models
+    for (const model of client.service.models.values()) {
+      handleServiceOrphanType(context, model);
+    }
+    // orphan enums
+    for (const enumType of client.service.enums.values()) {
+      handleServiceOrphanType(context, enumType);
+    }
+    // orphan unions
+    for (const unionType of client.service.unions.values()) {
+      handleServiceOrphanType(context, unionType);
+    }
+  }
   // update access
   updateAccessOfModel(context);
   // update spread model
diff --git a/packages/typespec-client-generator-core/test/types/multipart-types.test.ts b/packages/typespec-client-generator-core/test/types/multipart-types.test.ts
index b2a8f4141a..8ad3e632fa 100644
--- a/packages/typespec-client-generator-core/test/types/multipart-types.test.ts
+++ b/packages/typespec-client-generator-core/test/types/multipart-types.test.ts
@@ -619,4 +619,40 @@ describe("typespec-client-generator-core: multipart types", () => {
     strictEqual(nameProperty.name, "name");
     strictEqual((nameProperty as SdkBodyModelPropertyType).serializedName, "serializedName");
   });
+
+  it("multipart in client customization", async () => {
+    const testCode = [
+      `
+        @service({title: "Test Service"}) namespace TestService;
+        model MultiPartRequest {
+          profileImage: bytes;
+        }
+  
+        @post op multipartUse(@header contentType: "multipart/form-data", @body body: MultiPartRequest): NoContentResponse;
+    `,
+      `
+      namespace Customizations;
+      
+      @client({name: "FirstOrderClient", service: TestService})
+      interface FirstOrder {}
+
+      @client({name: "SecondOrderClient", service: TestService})
+      interface SecondOrder {
+        myOp is TestService.multipartUse
+      }
+    `,
+    ];
+
+    await runner.compileWithCustomization(testCode[0], testCode[1]);
+
+    const models = runner.context.sdkPackage.models;
+    const MultiPartRequest = models.find((x) => x.name === "MultiPartRequest");
+    ok(MultiPartRequest);
+    const property = MultiPartRequest.properties.find((x) => x.name === "profileImage");
+    ok(property);
+    strictEqual(property.kind, "property");
+    strictEqual(property.isMultipartFileInput, true);
+    ok(property.multipartOptions);
+    strictEqual(property.multipartOptions.isFilePart, true);
+  });
 });