diff --git a/templates/default/api.ejs b/templates/default/api.ejs
index a393c917..b631ba89 100644
--- a/templates/default/api.ejs
+++ b/templates/default/api.ejs
@@ -50,7 +50,7 @@ export class <%~ config.apiClassName %><SecurityDataType extends unknown><% if (
 <% if (routes.outOfModule) { %>
   <% for (const route of routes.outOfModule) { %>
 
-  <%~ includeFile('./procedure-call.ejs', { ...it, route }) %>
+  <%~ includeFile('./procedure-call.ejs', { ...it, route, isObjectProperty: false }) %>
 
   <% } %>
 <% } %>
@@ -60,7 +60,7 @@ export class <%~ config.apiClassName %><SecurityDataType extends unknown><% if (
   <%~ moduleName %> = {
   <% for (const route of combinedRoutes) { %>
 
-  <%~ includeFile('./procedure-call.ejs', { ...it, route }) %>
+  <%~ includeFile('./procedure-call.ejs', { ...it, route, isObjectProperty: true }) %>
 
   <% } %>
   }
diff --git a/templates/default/procedure-call.ejs b/templates/default/procedure-call.ejs
index 90af47bd..d197037e 100644
--- a/templates/default/procedure-call.ejs
+++ b/templates/default/procedure-call.ejs
@@ -1,5 +1,5 @@
 <%
-const { utils, route, config } = it;
+const { utils, route, config, isObjectProperty = route.namespace } = it;
 const { requestBodyInfo, responseBodyInfo, specificArgNameResolver } = route;
 const { _, getInlineParseContent, getParseContent, parseSchema, getComponentByRef, require } = utils;
 const { parameters, path, method, payload, query, formData, security, requestParams } = route.request;
@@ -90,7 +90,7 @@ const isValidIdentifier = (name) => /^[A-Za-z_$][A-Za-z0-9_$]*$/.test(name);
 <%~ routeDocs.lines %>
 
  */
-<% if (isValidIdentifier(route.routeName.usage)) { %><%~ route.routeName.usage %><%~ route.namespace ? ': ' : ' = ' %><% } else { %>"<%~ route.routeName.usage %>"<%~ route.namespace ? ': ' : ' = ' %><% } %>(<%~ wrapperArgs %>)<%~ config.toJS ? `: ${describeReturnType()}` : "" %> =>
+<% if (isValidIdentifier(route.routeName.usage)) { %><%~ route.routeName.usage %><%~ isObjectProperty ? ': ' : ' = ' %><% } else { %>"<%~ route.routeName.usage %>"<%~ isObjectProperty ? ': ' : ' = ' %><% } %>(<%~ wrapperArgs %>)<%~ config.toJS ? `: ${describeReturnType()}` : "" %> =>
     <%~ config.singleHttpClient ? 'this.http.request' : 'this.request' %><<%~ type %>, <%~ errorType %>>({
         path: `<%~ path %>`,
         method: '<%~ _.upperCase(method) %>',
diff --git a/templates/modular/api.ejs b/templates/modular/api.ejs
index 25bfa182..070f38b3 100644
--- a/templates/modular/api.ejs
+++ b/templates/modular/api.ejs
@@ -23,6 +23,6 @@ export class <%= apiClassName %><SecurityDataType = unknown><% if (!config.singl
 <% } %>
 
     <% for (const route of routes) { %>
-        <%~ includeFile('./procedure-call.ejs', { ...it, route }) %>
+        <%~ includeFile('./procedure-call.ejs', { ...it, route, isObjectProperty: false }) %>
     <% } %>
 }
diff --git a/templates/modular/procedure-call.ejs b/templates/modular/procedure-call.ejs
index 90af47bd..d197037e 100644
--- a/templates/modular/procedure-call.ejs
+++ b/templates/modular/procedure-call.ejs
@@ -1,5 +1,5 @@
 <%
-const { utils, route, config } = it;
+const { utils, route, config, isObjectProperty = route.namespace } = it;
 const { requestBodyInfo, responseBodyInfo, specificArgNameResolver } = route;
 const { _, getInlineParseContent, getParseContent, parseSchema, getComponentByRef, require } = utils;
 const { parameters, path, method, payload, query, formData, security, requestParams } = route.request;
@@ -90,7 +90,7 @@ const isValidIdentifier = (name) => /^[A-Za-z_$][A-Za-z0-9_$]*$/.test(name);
 <%~ routeDocs.lines %>
 
  */
-<% if (isValidIdentifier(route.routeName.usage)) { %><%~ route.routeName.usage %><%~ route.namespace ? ': ' : ' = ' %><% } else { %>"<%~ route.routeName.usage %>"<%~ route.namespace ? ': ' : ' = ' %><% } %>(<%~ wrapperArgs %>)<%~ config.toJS ? `: ${describeReturnType()}` : "" %> =>
+<% if (isValidIdentifier(route.routeName.usage)) { %><%~ route.routeName.usage %><%~ isObjectProperty ? ': ' : ' = ' %><% } else { %>"<%~ route.routeName.usage %>"<%~ isObjectProperty ? ': ' : ' = ' %><% } %>(<%~ wrapperArgs %>)<%~ config.toJS ? `: ${describeReturnType()}` : "" %> =>
     <%~ config.singleHttpClient ? 'this.http.request' : 'this.request' %><<%~ type %>, <%~ errorType %>>({
         path: `<%~ path %>`,
         method: '<%~ _.upperCase(method) %>',
diff --git a/tests/spec/typescript-syntax-fix/basic.test.ts b/tests/spec/typescript-syntax-fix/basic.test.ts
new file mode 100644
index 00000000..cc2c0a5f
--- /dev/null
+++ b/tests/spec/typescript-syntax-fix/basic.test.ts
@@ -0,0 +1,186 @@
+import * as fs from "node:fs/promises";
+import * as os from "node:os";
+import * as path from "node:path";
+import { afterAll, beforeAll, describe, expect, test } from "vitest";
+import { generateApi } from "../../../src/index.js";
+
+describe("TypeScript syntax fix for operationIds starting with numbers", async () => {
+  let tmpdir: string;
+
+  beforeAll(async () => {
+    tmpdir = await fs.mkdtemp(path.join(os.tmpdir(), "swagger-typescript-api"));
+  });
+
+  afterAll(async () => {
+    await fs.rm(tmpdir, { recursive: true });
+  });
+
+  test("should use assignment syntax for direct class methods", async () => {
+    const schema = {
+      "openapi": "3.0.0",
+      "info": {
+        "title": "Test API",
+        "version": "1.0.0"
+      },
+      "paths": {
+        "/": {
+          "get": {
+            "operationId": "123getUser",
+            "summary": "Get user with operationId starting with number",
+            "responses": {
+              "200": {
+                "description": "OK",
+                "content": {
+                  "application/json": {
+                    "schema": {
+                      "type": "object",
+                      "properties": {
+                        "id": { "type": "integer" },
+                        "name": { "type": "string" }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    };
+
+    const schemaPath = path.join(tmpdir, "direct-method-schema.json");
+    await fs.writeFile(schemaPath, JSON.stringify(schema, null, 2));
+
+    await generateApi({
+      fileName: "direct-method",
+      input: schemaPath,
+      output: tmpdir,
+      silent: true,
+      generateClient: true,
+    });
+
+    const content = await fs.readFile(path.join(tmpdir, "direct-method.ts"), {
+      encoding: "utf8",
+    });
+
+    // Should use assignment syntax for direct class methods
+    expect(content).toContain('"123GetUser" = ');
+    // Should not use colon syntax for direct class methods
+    expect(content).not.toContain('"123GetUser": ');
+  });
+
+  test("should use colon syntax for object properties", async () => {
+    const schema = {
+      "openapi": "3.0.0",
+      "info": {
+        "title": "Test API",
+        "version": "1.0.0"
+      },
+      "paths": {
+        "/api/user/{id}": {
+          "get": {
+            "operationId": "456getUser",
+            "summary": "Get user with operationId starting with number",
+            "tags": ["Users"],
+            "parameters": [
+              {
+                "name": "id",
+                "in": "path",
+                "required": true,
+                "schema": {
+                  "type": "integer"
+                }
+              }
+            ],
+            "responses": {
+              "200": {
+                "description": "OK",
+                "content": {
+                  "application/json": {
+                    "schema": {
+                      "type": "object",
+                      "properties": {
+                        "id": { "type": "integer" },
+                        "name": { "type": "string" }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    };
+
+    const schemaPath = path.join(tmpdir, "object-property-schema.json");
+    await fs.writeFile(schemaPath, JSON.stringify(schema, null, 2));
+
+    await generateApi({
+      fileName: "object-property",
+      input: schemaPath,
+      output: tmpdir,
+      silent: true,
+      generateClient: true,
+    });
+
+    const content = await fs.readFile(path.join(tmpdir, "object-property.ts"), {
+      encoding: "utf8",
+    });
+
+    // Should use colon syntax for object properties
+    expect(content).toContain('"456GetUser": ');
+    // Should not use assignment syntax for object properties
+    expect(content).not.toContain('"456GetUser" = ');
+  });
+
+  test("should handle normal identifiers correctly", async () => {
+    const schema = {
+      "openapi": "3.0.0",
+      "info": {
+        "title": "Test API",
+        "version": "1.0.0"
+      },
+      "paths": {
+        "/": {
+          "get": {
+            "operationId": "normalMethod",
+            "summary": "Normal method",
+            "responses": {
+              "200": {
+                "description": "OK",
+                "content": {
+                  "application/json": {
+                    "schema": {
+                      "type": "object"
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    };
+
+    const schemaPath = path.join(tmpdir, "normal-method-schema.json");
+    await fs.writeFile(schemaPath, JSON.stringify(schema, null, 2));
+
+    await generateApi({
+      fileName: "normal-method",
+      input: schemaPath,
+      output: tmpdir,
+      silent: true,
+      generateClient: true,
+    });
+
+    const content = await fs.readFile(path.join(tmpdir, "normal-method.ts"), {
+      encoding: "utf8",
+    });
+
+    // Should use assignment syntax for direct class methods (no quotes needed)
+    expect(content).toContain('normalMethod = ');
+    // Should not use colon syntax for direct class methods
+    expect(content).not.toContain('normalMethod: ');
+  });
+});
\ No newline at end of file