diff --git a/src/utils/is-arguments.ts b/src/utils/is-arguments.ts
index 265e042..57ae7ad 100644
--- a/src/utils/is-arguments.ts
+++ b/src/utils/is-arguments.ts
@@ -6,6 +6,6 @@ import { getTagString } from './get-tag-string';
  * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/arguments
  * @returns `true` if `o` is a function's array-like `arguments` variable
  */
-export function isArguments(o: any): boolean {
+export function isArguments(o: unknown): o is IArguments {
    return getTagString(o) === '[object Arguments]';
 }
diff --git a/src/utils/is-array-of-strings.ts b/src/utils/is-array-of-strings.ts
index 70e65ae..7efeaa2 100644
--- a/src/utils/is-array-of-strings.ts
+++ b/src/utils/is-array-of-strings.ts
@@ -8,7 +8,7 @@ import { isString } from './is-string';
  * not counted as `string` values, even if the TypeScript compiler's `strictNullChecks`
  * flag is set to `false` in your project.
  */
-export function isArrayOfStrings(values: any): values is string[] {
+export function isArrayOfStrings(values: unknown): values is string[] {
    if (!isArray(values)) {
       return false;
    }
diff --git a/src/utils/is-array.ts b/src/utils/is-array.ts
index d4ac950..59f7749 100644
--- a/src/utils/is-array.ts
+++ b/src/utils/is-array.ts
@@ -3,6 +3,6 @@
  *
  * @returns `true` if `o` is an `Array`, regardless of the types that it contains
  */
-export function isArray(o: any): o is unknown[] {
+export function isArray(o: unknown): o is unknown[] {
    return Array.isArray(o);
 }
diff --git a/src/utils/is-enum-value.ts b/src/utils/is-enum-value.ts
index 0951c4e..12fa9c2 100644
--- a/src/utils/is-enum-value.ts
+++ b/src/utils/is-enum-value.ts
@@ -1,7 +1,7 @@
 /**
  * Type guard to check to see if the given value is a valid value for the enum.
  */
-export function isEnumValue<T>(enumType: T, value: any): value is T[keyof T] {
+export function isEnumValue<T>(enumType: T, value: unknown): value is T[keyof T] {
    return (Object.keys(enumType) as Array<keyof T>)
       .map((key) => {
          return enumType[key];
diff --git a/src/utils/is-number.ts b/src/utils/is-number.ts
index 5a85103..9801fba 100644
--- a/src/utils/is-number.ts
+++ b/src/utils/is-number.ts
@@ -8,6 +8,6 @@ import { isObject } from './is-object';
  * considered `number`s. If you need to check for one of those values, you can use the
  * built-in `Number.isNaN` or `Number.isFinite` functions.
  */
-export function isNumber(o: any): o is number {
+export function isNumber(o: unknown): o is number {
    return typeof o === 'number' || (isObject(o) && getTagString(o) === '[object Number]');
 }
diff --git a/src/utils/is-object.ts b/src/utils/is-object.ts
index 0592825..3e2ef27 100644
--- a/src/utils/is-object.ts
+++ b/src/utils/is-object.ts
@@ -9,7 +9,7 @@
  * @see https://github.com/jashkenas/underscore/blob/d5fe0fd4060f13b40608cb9d92eda6d857e8752c/underscore.js#L1322
  * @returns `true` if `o` is an `object`
  */
-export function isObject(o: any): o is object {
+export function isObject(o: unknown): o is object {
    let type = typeof o;
 
    return o !== null && (type === 'object' || type === 'function');
diff --git a/src/utils/is-promise-like.ts b/src/utils/is-promise-like.ts
index 5dca394..6b91543 100644
--- a/src/utils/is-promise-like.ts
+++ b/src/utils/is-promise-like.ts
@@ -8,6 +8,6 @@ import { isObject } from './is-object';
  *
  * @returns `true` if `o` is `Promise`-like (i.e. has a `then` function)
  */
-export function isPromiseLike(o: any): o is PromiseLike<unknown> {
+export function isPromiseLike(o: unknown): o is PromiseLike<unknown> {
    return isPromise(o) || (isObject(o) && typeof (o as any).then === 'function');
 }
diff --git a/src/utils/is-promise.ts b/src/utils/is-promise.ts
index 3435381..8989925 100644
--- a/src/utils/is-promise.ts
+++ b/src/utils/is-promise.ts
@@ -6,6 +6,6 @@ import { getTagString } from './get-tag-string';
  *
  * @returns `true` if `o` is a `Promise`
  */
-export function isPromise(o: any): o is Promise<unknown> {
+export function isPromise(o: unknown): o is Promise<unknown> {
    return isObject(o) && getTagString(o) === '[object Promise]';
 }
diff --git a/src/utils/is-string.ts b/src/utils/is-string.ts
index 411b3e0..617e1d0 100644
--- a/src/utils/is-string.ts
+++ b/src/utils/is-string.ts
@@ -8,6 +8,6 @@ import { getTagString } from './get-tag-string';
  * `string` values, even if the TypeScript compiler's `strictNullChecks` flag is set to
  * `false` in your project.
  */
-export function isString(o: any): o is string {
+export function isString(o: unknown): o is string {
    return typeof o === 'string' || (isObject(o) && getTagString(o) === '[object String]');
 }