diff --git a/packages/mountable/src/options.test.ts b/packages/mountable/src/options.test.ts
index d26f5049c..84dcb4da4 100644
--- a/packages/mountable/src/options.test.ts
+++ b/packages/mountable/src/options.test.ts
@@ -68,8 +68,15 @@ describe("parseMountOptions()", () => {
     });
   });
 
-  it("fills `entrypoint`, and `requirements` fields and converts the `files` into the canonical form", () => {
+  it("throws an error if the `entrypoint` option is not provided", () => {
+    expect(() => parseMountOptions({})).toThrowError(
+      "The `entrypoint` field is required.",
+    );
+  });
+
+  it("fills the `requirements` field and converts the `files` into the canonical form", () => {
     const { kernelOptions } = parseMountOptions({
+      entrypoint: "streamlit_app.py",
       files: {
         "streamlit_app.py": "foo",
         "foo.txt": {
@@ -101,6 +108,7 @@ describe("parseMountOptions()", () => {
 
   it("normalizes the archives field", () => {
     const { kernelOptions } = parseMountOptions({
+      entrypoint: "app.py",
       archives: [
         {
           url: "./foo.zip",
@@ -120,7 +128,7 @@ describe("parseMountOptions()", () => {
       ],
     });
     expect(kernelOptions).toEqual({
-      entrypoint: "streamlit_app.py",
+      entrypoint: "app.py",
       requirements: [],
       prebuiltPackageNames: [],
       files: {},
@@ -167,11 +175,12 @@ describe("parseMountOptions()", () => {
   it("preserves the `requirements` option if specified", () => {
     const { kernelOptions } = parseMountOptions({
       requirements: ["matplotlib"],
+      entrypoint: "app.py",
     });
     expect(kernelOptions).toEqual({
       requirements: ["matplotlib"],
       prebuiltPackageNames: [],
-      entrypoint: "streamlit_app.py",
+      entrypoint: "app.py",
       files: {},
       archives: [],
     });
@@ -180,11 +189,12 @@ describe("parseMountOptions()", () => {
   it("preserves the `prebuiltPackageNames` option if specified", () => {
     const { kernelOptions } = parseMountOptions({
       prebuiltPackageNames: ["openssl"],
+      entrypoint: "foo.py",
     });
     expect(kernelOptions).toEqual({
       requirements: [],
       prebuiltPackageNames: ["openssl"],
-      entrypoint: "streamlit_app.py",
+      entrypoint: "foo.py",
       files: {},
       archives: [],
     });
@@ -200,6 +210,7 @@ describe("parseMountOptions()", () => {
 
   it("passes the toast callback options", () => {
     const { toastCallbackOptions } = parseMountOptions({
+      entrypoint: "foo.py",
       disableProgressToasts: true,
       disableErrorToasts: true,
     });
diff --git a/packages/mountable/src/options.ts b/packages/mountable/src/options.ts
index 6e1838e51..f5970a73e 100644
--- a/packages/mountable/src/options.ts
+++ b/packages/mountable/src/options.ts
@@ -5,20 +5,23 @@ import type {
 } from "@stlite/kernel";
 import type { MakeToastKernelCallbacksOptions } from "@stlite/common-react";
 
-export interface SimplifiedStliteKernelOptions {
-  entrypoint?: string;
-  requirements?: StliteKernelOptions["requirements"];
-  prebuiltPackageNames?: StliteKernelOptions["prebuiltPackageNames"];
-  files?: Record<
+// Simplified version of StliteKernelOptions for the mount function.
+// This is exposed to non-typed consumers of the mount function,
+// so all fields are typed as optional.
+export type SimplifiedStliteKernelOptions = Partial<{
+  entrypoint: string;
+  requirements: StliteKernelOptions["requirements"];
+  prebuiltPackageNames: StliteKernelOptions["prebuiltPackageNames"];
+  files: Record<
     string,
     EmscriptenFile | EmscriptenFileUrl | EmscriptenFile["data"] // EmscriptenFile["data"] is allowed as a shorthand for convenience.
   >;
-  archives?: StliteKernelOptions["archives"];
-  hostConfig?: StliteKernelOptions["hostConfigResponse"];
-  pyodideUrl?: StliteKernelOptions["pyodideUrl"];
-  streamlitConfig?: StliteKernelOptions["streamlitConfig"];
-  idbfsMountpoints?: StliteKernelOptions["idbfsMountpoints"];
-}
+  archives: StliteKernelOptions["archives"];
+  hostConfig: StliteKernelOptions["hostConfigResponse"];
+  pyodideUrl: StliteKernelOptions["pyodideUrl"];
+  streamlitConfig: StliteKernelOptions["streamlitConfig"];
+  idbfsMountpoints: StliteKernelOptions["idbfsMountpoints"];
+}>;
 
 function canonicalizeFiles(
   files: SimplifiedStliteKernelOptions["files"],
@@ -111,9 +114,15 @@ export function parseMountOptions(options: MountOptions): {
   const files = canonicalizeFiles(options.files);
   const archives = canonicalizeArchives(options.archives);
 
+  // TODO: Validate the options object using superstruct.
+  const entrypoint = options.entrypoint;
+  if (entrypoint == null) {
+    throw new Error("The `entrypoint` field is required.");
+  }
+
   return {
     kernelOptions: {
-      entrypoint: options.entrypoint || DEFAULT_ENTRYPOINT,
+      entrypoint,
       files,
       archives,
       requirements: options.requirements || [],