diff --git a/deno/lib/__tests__/custom.test.ts b/deno/lib/__tests__/custom.test.ts
index a6f20bad9..ff8b9577c 100644
--- a/deno/lib/__tests__/custom.test.ts
+++ b/deno/lib/__tests__/custom.test.ts
@@ -9,3 +9,11 @@ test("passing validations", () => {
   example1.parse(1234);
   expect(() => example1.parse({})).toThrow();
 });
+
+test("string params", () => {
+  const example1 = z.custom<number>((x) => typeof x !== "number", "customerr");
+  const result = example1.safeParse(1234);
+  expect(result.success).toEqual(false);
+  // @ts-ignore
+  expect(JSON.stringify(result.error)).toContain("customerr");
+});
diff --git a/deno/lib/helpers/util.ts b/deno/lib/helpers/util.ts
index 21fe37338..85419b695 100644
--- a/deno/lib/helpers/util.ts
+++ b/deno/lib/helpers/util.ts
@@ -114,7 +114,7 @@ export namespace objectUtil {
     T extends object,
     R extends keyof T = requiredKeys<T>
     // O extends keyof T = optionalKeys<T>
-  > = Pick<T, R> & Partial<T>;
+  > = Pick<Required<T>, R> & Partial<T>;
   //  = { [k in O]?: T[k] } & { [k in R]: T[k] };
 
   export type identity<T> = T;
diff --git a/deno/lib/types.ts b/deno/lib/types.ts
index 7b3ee92cb..8606ba0ba 100644
--- a/deno/lib/types.ts
+++ b/deno/lib/types.ts
@@ -4743,14 +4743,28 @@ export class ZodPipeline<
 type CustomParams = CustomErrorParams & { fatal?: boolean };
 export const custom = <T>(
   check?: (data: unknown) => any,
-  params: CustomParams | ((input: any) => CustomParams) = {},
-  /* @deprecated */
+  params: string | CustomParams | ((input: any) => CustomParams) = {},
+  /*
+   * @deprecated
+   *
+   * Pass `fatal` into the params object instead:
+   *
+   * ```ts
+   * z.string().custom((val) => val.length > 5, { fatal: false })
+   * ```
+   *
+   */
   fatal?: boolean
 ): ZodType<T> => {
   if (check)
     return ZodAny.create().superRefine((data, ctx) => {
       if (!check(data)) {
-        const p = typeof params === "function" ? params(data) : params;
+        const p =
+          typeof params === "function"
+            ? params(data)
+            : typeof params === "string"
+            ? { message: params }
+            : params;
         const _fatal = p.fatal ?? fatal ?? true;
         const p2 = typeof p === "string" ? { message: p } : p;
         ctx.addIssue({ code: "custom", ...p2, fatal: _fatal });
diff --git a/package.json b/package.json
index 9a44f634a..2f47ce4fb 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "zod",
-  "version": "3.21.3",
+  "version": "3.21.4",
   "author": "Colin McDonnell <colin@colinhacks.com>",
   "repository": {
     "type": "git",
diff --git a/playground.ts b/playground.ts
index b22662a96..d17b18eb4 100644
--- a/playground.ts
+++ b/playground.ts
@@ -1,18 +1,2 @@
 import { z } from "./src";
 z;
-
-const baseCategorySchema = z.object({
-  name: z.string().brand("CategoryName"),
-});
-
-type CategoryInput = z.input<typeof baseCategorySchema> & {
-  subcategories: CategoryInput[];
-};
-type CategoryOutput = z.output<typeof baseCategorySchema> & {
-  subcategories: CategoryOutput[];
-};
-
-const categorySchema: z.ZodType<CategoryOutput, any, CategoryInput> =
-  baseCategorySchema.extend({
-    subcategories: z.lazy(() => categorySchema.array()),
-  });
diff --git a/src/__tests__/custom.test.ts b/src/__tests__/custom.test.ts
index 6a3eb2858..7292a87a6 100644
--- a/src/__tests__/custom.test.ts
+++ b/src/__tests__/custom.test.ts
@@ -8,3 +8,11 @@ test("passing validations", () => {
   example1.parse(1234);
   expect(() => example1.parse({})).toThrow();
 });
+
+test("string params", () => {
+  const example1 = z.custom<number>((x) => typeof x !== "number", "customerr");
+  const result = example1.safeParse(1234);
+  expect(result.success).toEqual(false);
+  // @ts-ignore
+  expect(JSON.stringify(result.error)).toContain("customerr");
+});
diff --git a/src/helpers/util.ts b/src/helpers/util.ts
index 21fe37338..85419b695 100644
--- a/src/helpers/util.ts
+++ b/src/helpers/util.ts
@@ -114,7 +114,7 @@ export namespace objectUtil {
     T extends object,
     R extends keyof T = requiredKeys<T>
     // O extends keyof T = optionalKeys<T>
-  > = Pick<T, R> & Partial<T>;
+  > = Pick<Required<T>, R> & Partial<T>;
   //  = { [k in O]?: T[k] } & { [k in R]: T[k] };
 
   export type identity<T> = T;
diff --git a/src/types.ts b/src/types.ts
index 81c2dcde5..5a99d04b9 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -4743,14 +4743,28 @@ export class ZodPipeline<
 type CustomParams = CustomErrorParams & { fatal?: boolean };
 export const custom = <T>(
   check?: (data: unknown) => any,
-  params: CustomParams | ((input: any) => CustomParams) = {},
-  /* @deprecated */
+  params: string | CustomParams | ((input: any) => CustomParams) = {},
+  /*
+   * @deprecated
+   *
+   * Pass `fatal` into the params object instead:
+   *
+   * ```ts
+   * z.string().custom((val) => val.length > 5, { fatal: false })
+   * ```
+   *
+   */
   fatal?: boolean
 ): ZodType<T> => {
   if (check)
     return ZodAny.create().superRefine((data, ctx) => {
       if (!check(data)) {
-        const p = typeof params === "function" ? params(data) : params;
+        const p =
+          typeof params === "function"
+            ? params(data)
+            : typeof params === "string"
+            ? { message: params }
+            : params;
         const _fatal = p.fatal ?? fatal ?? true;
         const p2 = typeof p === "string" ? { message: p } : p;
         ctx.addIssue({ code: "custom", ...p2, fatal: _fatal });