diff --git a/typegate/tests/runtimes/deno/deno_test.ts b/typegate/tests/runtimes/deno/deno_test.ts
index 927788548..ad365139a 100644
--- a/typegate/tests/runtimes/deno/deno_test.ts
+++ b/typegate/tests/runtimes/deno/deno_test.ts
@@ -141,12 +141,12 @@ Meta.test("Deno runtime with typescript", async (t) => {
     await gql`
       query {
         hello(name: "World")
-        helloFn(name: "World!")
+        helloFn(name: "wOrLd")
       }
     `
       .expectData({
         hello: "Hello World",
-        helloFn: "Hello World!",
+        helloFn: "Hello world",
       })
       .on(e);
   });
diff --git a/typegate/tests/runtimes/deno/deno_typescript.ts b/typegate/tests/runtimes/deno/deno_typescript.ts
index 5799a7209..20815d20f 100644
--- a/typegate/tests/runtimes/deno/deno_typescript.ts
+++ b/typegate/tests/runtimes/deno/deno_typescript.ts
@@ -6,10 +6,10 @@ import { DenoRuntime } from "@typegraph/sdk/runtimes/deno.js";
 
 const hello = ({ name }: any) => `Hello ${name}`;
 function helloFn({ name }: any) {
-  return `Hello ${name}`;
+  return `Hello ${(name as string).toLowerCase()}`;
 }
 
-typegraph("test-deno-static", (g: any) => {
+typegraph("test-deno-tyepscript", (g: any) => {
   const deno = new DenoRuntime();
   const pub = Policy.public();
 
diff --git a/typegraph/node/sdk/src/runtimes/deno.ts b/typegraph/node/sdk/src/runtimes/deno.ts
index 605c07e1c..fd3c17e10 100644
--- a/typegraph/node/sdk/src/runtimes/deno.ts
+++ b/typegraph/node/sdk/src/runtimes/deno.ts
@@ -39,7 +39,23 @@ export interface DenoImport {
 }
 
 function stringifyFn(code: string | Function) {
-  return typeof code == "function" ? code.toString() : code;
+  if (typeof code == "function") {
+    const source = code.toString();
+    const namedFnMatch = source.match(/function\s*(\*?\s*[a-zA-Z0-9_]+)/);
+    if (namedFnMatch) {
+      const [, name] = namedFnMatch;
+      if (name.replace(/s/g, "").startsWith("*")) {
+        throw new Error(`Generator function "${name}" not supported`);
+      }
+      if (/function\s[a-zA-Z0-9_]+\(\) { \[native code\] }/.test(source)) {
+        throw new Error(
+          `"${name}" is not supported as it is a native function`,
+        );
+      }
+    }
+    return source;
+  }
+  return code;
 }
 
 export class DenoRuntime extends Runtime {