diff --git a/src/cli-options.ts b/src/cli-options.ts
index be820661..9822b034 100755
--- a/src/cli-options.ts
+++ b/src/cli-options.ts
@@ -615,7 +615,7 @@ const cliOptions: CLIOption[] = [
       'Check one or more sections of dependencies only: dev, optional, peer, prod, or packageManager (comma-delimited).',
     default: ['prod', 'dev', 'optional', 'packageManager'],
     parse: value => (value && typeof value === 'string' ? value.split(',') : value),
-    type: 'string | string[]',
+    type: 'string | readonly string[]',
   },
   {
     long: 'deprecated',
@@ -666,7 +666,7 @@ const cliOptions: CLIOption[] = [
     arg: 'p',
     description:
       'Include only package names matching the given string, wildcard, glob, comma-or-space-delimited list, /regex/, or predicate function.',
-    type: 'string | RegExp | (string | RegExp)[] | FilterFunction',
+    type: 'string | RegExp | readonly (string | RegExp)[] | FilterFunction',
     parse: (value, accum) => [...(accum || []), value],
     help: extendedHelpFilterFunction,
   },
@@ -682,7 +682,7 @@ const cliOptions: CLIOption[] = [
     long: 'filterVersion',
     arg: 'p',
     description: 'Filter on package version using comma-or-space-delimited list, /regex/, or predicate function.',
-    type: 'string | RegExp | (string | RegExp)[] | FilterFunction',
+    type: 'string | RegExp | readonly (string | RegExp)[] | FilterFunction',
     parse: (value, accum) => [...(accum || []), value],
     help: extendedHelpFilterVersionFunction,
   },
@@ -693,7 +693,7 @@ const cliOptions: CLIOption[] = [
       'Modify the output formatting or show additional information. Specify one or more comma-delimited values: group, ownerChanged, repo, time, lines, installedVersion.',
     parse: value => (typeof value === 'string' ? value.split(',') : value),
     default: [],
-    type: 'string[]',
+    type: 'readonly string[]',
     choices: ['group', 'ownerChanged', 'repo', 'time', 'lines', 'installedVersion'],
     help: extendedHelpFormat,
   },
@@ -824,7 +824,7 @@ const cliOptions: CLIOption[] = [
     arg: 'p',
     description:
       'Exclude packages matching the given string, wildcard, glob, comma-or-space-delimited list, /regex/, or predicate function.',
-    type: 'string | RegExp | (string | RegExp)[] | FilterFunction',
+    type: 'string | RegExp | readonly (string | RegExp)[] | FilterFunction',
     parse: (value, accum) => [...(accum || []), value],
     help: extendedHelpRejectFunction,
   },
@@ -832,7 +832,7 @@ const cliOptions: CLIOption[] = [
     long: 'rejectVersion',
     arg: 'p',
     description: 'Exclude package.json versions using comma-or-space-delimited list, /regex/, or predicate function.',
-    type: 'string | RegExp | (string | RegExp)[] | FilterFunction',
+    type: 'string | RegExp | readonly (string | RegExp)[] | FilterFunction',
     parse: (value, accum) => [...(accum || []), value],
     help: extendedHelpRejectVersionFunction,
   },
@@ -901,7 +901,7 @@ const cliOptions: CLIOption[] = [
     parse: (value, accum) => [...accum, value],
     default: [],
     description: 'Run on one or more specified workspaces. Add `--root` to also upgrade the root project.',
-    type: 'string[]',
+    type: 'readonly string[]',
   },
   {
     long: 'workspaces',
diff --git a/src/lib/logging.ts b/src/lib/logging.ts
index 82683b77..04feef8b 100755
--- a/src/lib/logging.ts
+++ b/src/lib/logging.ts
@@ -158,7 +158,7 @@ export async function toDependencyTable({
 }: {
   from: Index<VersionSpec>
   to: Index<VersionSpec>
-  format?: string[]
+  format?: readonly string[]
   ownersChangedDeps?: Index<boolean>
   /** See: logging/getPackageRepo pkgFile param. */
   pkgFile?: string
diff --git a/src/lib/resolveDepSections.ts b/src/lib/resolveDepSections.ts
index 6076918a..2c7ab4c5 100644
--- a/src/lib/resolveDepSections.ts
+++ b/src/lib/resolveDepSections.ts
@@ -11,7 +11,7 @@ const depAliases: Index<keyof PackageFile> = {
 }
 
 /** Gets a list of dependency sections based on options.dep. */
-const resolveDepSections = (dep?: string | string[]): (keyof PackageFile)[] => {
+const resolveDepSections = (dep?: string | readonly string[]): (keyof PackageFile)[] => {
   // parse dep string and set default
   const depOptions: string[] = dep ? (typeof dep === 'string' ? dep.split(',') : dep) : cliOptionsMap.dep.default
 
diff --git a/src/types/FilterPattern.ts b/src/types/FilterPattern.ts
index 6891bc48..dd18bcb1 100644
--- a/src/types/FilterPattern.ts
+++ b/src/types/FilterPattern.ts
@@ -1,4 +1,4 @@
 import { FilterFunction } from './FilterFunction'
 
 /** Supported patterns for the --filter and --reject options. */
-export type FilterPattern = string | RegExp | (string | RegExp)[] | FilterFunction
+export type FilterPattern = string | RegExp | readonly (string | RegExp)[] | FilterFunction
diff --git a/src/types/RunOptions.ts b/src/types/RunOptions.ts
index 95be127f..a621ce87 100644
--- a/src/types/RunOptions.ts
+++ b/src/types/RunOptions.ts
@@ -50,7 +50,7 @@ export interface RunOptions {
    *
    * @default ["prod","dev","optional","packageManager"]
    */
-  dep?: string | string[]
+  dep?: string | readonly string[]
 
   /** Include deprecated packages. Use `--no-deprecated` to exclude deprecated packages (uses more bandwidth).
    *
@@ -77,16 +77,16 @@ export interface RunOptions {
   errorLevel?: number
 
   /** Include only package names matching the given string, wildcard, glob, comma-or-space-delimited list, /regex/, or predicate function. Run "ncu --help --filter" for details. */
-  filter?: string | RegExp | (string | RegExp)[] | FilterFunction
+  filter?: string | RegExp | readonly (string | RegExp)[] | FilterFunction
 
   /** Filters out upgrades based on a user provided function. Run "ncu --help --filterResults" for details. */
   filterResults?: FilterResultsFunction
 
   /** Filter on package version using comma-or-space-delimited list, /regex/, or predicate function. Run "ncu --help --filterVersion" for details. */
-  filterVersion?: string | RegExp | (string | RegExp)[] | FilterFunction
+  filterVersion?: string | RegExp | readonly (string | RegExp)[] | FilterFunction
 
   /** Modify the output formatting or show additional information. Specify one or more comma-delimited values: group, ownerChanged, repo, time, lines, installedVersion. Run "ncu --help --format" for details. */
-  format?: string[]
+  format?: readonly string[]
 
   /** Check global packages instead of in the current project. */
   global?: boolean
@@ -149,10 +149,10 @@ export interface RunOptions {
   registryType?: 'npm' | 'json'
 
   /** Exclude packages matching the given string, wildcard, glob, comma-or-space-delimited list, /regex/, or predicate function. Run "ncu --help --reject" for details. */
-  reject?: string | RegExp | (string | RegExp)[] | FilterFunction
+  reject?: string | RegExp | readonly (string | RegExp)[] | FilterFunction
 
   /** Exclude package.json versions using comma-or-space-delimited list, /regex/, or predicate function. Run "ncu --help --rejectVersion" for details. */
-  rejectVersion?: string | RegExp | (string | RegExp)[] | FilterFunction
+  rejectVersion?: string | RegExp | readonly (string | RegExp)[] | FilterFunction
 
   /** Remove version ranges from the final package version. */
   removeRange?: boolean
@@ -188,7 +188,7 @@ export interface RunOptions {
   verbose?: boolean
 
   /** Run on one or more specified workspaces. Add `--root` to also upgrade the root project. */
-  workspace?: string[]
+  workspace?: readonly string[]
 
   /** Run on all workspaces. Add `--root` to also upgrade the root project. */
   workspaces?: boolean