diff --git a/src/Bundle.ts b/src/Bundle.ts
index 6c23f85d34e..380d1dfebf5 100644
--- a/src/Bundle.ts
+++ b/src/Bundle.ts
@@ -104,7 +104,7 @@ export default class Bundle {
 	}
 
 	private async addManualChunks(
-		manualChunks: Record<string, string[]>
+		manualChunks: Record<string, readonly string[]>
 	): Promise<Map<Module, string>> {
 		const manualChunkAliasByEntry = new Map<Module, string>();
 		const chunkEntries = await Promise.all(
diff --git a/src/Chunk.ts b/src/Chunk.ts
index 437c7400145..bdaa1d76a72 100644
--- a/src/Chunk.ts
+++ b/src/Chunk.ts
@@ -165,13 +165,13 @@ export default class Chunk {
 	private strictFacade = false;
 	private usedModules: Module[] = undefined as never;
 	constructor(
-		private readonly orderedModules: Module[],
+		private readonly orderedModules: readonly Module[],
 		private readonly inputOptions: NormalizedInputOptions,
 		private readonly outputOptions: NormalizedOutputOptions,
-		private readonly unsetOptions: Set<string>,
+		private readonly unsetOptions: ReadonlySet<string>,
 		private readonly pluginDriver: PluginDriver,
-		private readonly modulesById: Map<string, Module | ExternalModule>,
-		private readonly chunkByModule: Map<Module, Chunk>,
+		private readonly modulesById: ReadonlyMap<string, Module | ExternalModule>,
+		private readonly chunkByModule: ReadonlyMap<Module, Chunk>,
 		private readonly facadeChunkByModule: Map<Module, Chunk>,
 		private readonly includedNamespaces: Set<Module>,
 		private readonly manualChunkAlias: string | null
@@ -209,10 +209,10 @@ export default class Chunk {
 	private static generateFacade(
 		inputOptions: NormalizedInputOptions,
 		outputOptions: NormalizedOutputOptions,
-		unsetOptions: Set<string>,
+		unsetOptions: ReadonlySet<string>,
 		pluginDriver: PluginDriver,
-		modulesById: Map<string, Module | ExternalModule>,
-		chunkByModule: Map<Module, Chunk>,
+		modulesById: ReadonlyMap<string, Module | ExternalModule>,
+		chunkByModule: ReadonlyMap<Module, Chunk>,
 		facadeChunkByModule: Map<Module, Chunk>,
 		includedNamespaces: Set<Module>,
 		facadedModule: Module,
diff --git a/src/ast/scopes/ChildScope.ts b/src/ast/scopes/ChildScope.ts
index 96ca9d95c67..cc679dce13c 100644
--- a/src/ast/scopes/ChildScope.ts
+++ b/src/ast/scopes/ChildScope.ts
@@ -51,8 +51,8 @@ export default class ChildScope extends Scope {
 	addUsedOutsideNames(
 		usedNames: Set<string>,
 		format: InternalModuleFormat,
-		exportNamesByVariable: ReadonlyMap<Variable, string[]>,
-		accessedGlobalsByScope: ReadonlyMap<ChildScope, Set<string>>
+		exportNamesByVariable: ReadonlyMap<Variable, readonly string[]>,
+		accessedGlobalsByScope: ReadonlyMap<ChildScope, ReadonlySet<string>>
 	): void {
 		for (const variable of this.accessedOutsideVariables.values()) {
 			if (variable.included) {
@@ -76,8 +76,8 @@ export default class ChildScope extends Scope {
 
 	deconflict(
 		format: InternalModuleFormat,
-		exportNamesByVariable: ReadonlyMap<Variable, string[]>,
-		accessedGlobalsByScope: ReadonlyMap<ChildScope, Set<string>>
+		exportNamesByVariable: ReadonlyMap<Variable, readonly string[]>,
+		accessedGlobalsByScope: ReadonlyMap<ChildScope, ReadonlySet<string>>
 	): void {
 		const usedNames = new Set<string>();
 		this.addUsedOutsideNames(usedNames, format, exportNamesByVariable, accessedGlobalsByScope);
diff --git a/src/ast/scopes/ModuleScope.ts b/src/ast/scopes/ModuleScope.ts
index e6e328a7b89..a264626885c 100644
--- a/src/ast/scopes/ModuleScope.ts
+++ b/src/ast/scopes/ModuleScope.ts
@@ -33,8 +33,8 @@ export default class ModuleScope extends ChildScope {
 
 	deconflict(
 		format: InternalModuleFormat,
-		exportNamesByVariable: ReadonlyMap<Variable, string[]>,
-		accessedGlobalsByScope: ReadonlyMap<ChildScope, Set<string>>
+		exportNamesByVariable: ReadonlyMap<Variable, readonly string[]>,
+		accessedGlobalsByScope: ReadonlyMap<ChildScope, ReadonlySet<string>>
 	): void {
 		// all module level variables are already deconflicted when deconflicting the chunk
 		for (const scope of this.children)
diff --git a/src/utils/PluginDriver.ts b/src/utils/PluginDriver.ts
index b96b54880b1..d2515287c9e 100644
--- a/src/utils/PluginDriver.ts
+++ b/src/utils/PluginDriver.ts
@@ -83,7 +83,7 @@ export class PluginDriver {
 	private readonly fileEmitter: FileEmitter;
 	private readonly pluginCache: Record<string, SerializablePluginCache> | undefined;
 	private readonly pluginContexts = new Map<Plugin, PluginContext>();
-	private readonly plugins: Plugin[];
+	private readonly plugins: readonly Plugin[];
 
 	constructor(
 		private readonly graph: Graph,
diff --git a/src/utils/chunkAssignment.ts b/src/utils/chunkAssignment.ts
index a8b340f8c9c..4a42e3da78a 100644
--- a/src/utils/chunkAssignment.ts
+++ b/src/utils/chunkAssignment.ts
@@ -29,7 +29,7 @@ export function getChunkAssignments(
 
 	function assignEntryToStaticDependencies(
 		entry: Module,
-		dynamicDependentEntryPoints: Set<Module> | null
+		dynamicDependentEntryPoints: ReadonlySet<Module> | null
 	) {
 		const modulesToHandle = new Set([entry]);
 		for (const module of modulesToHandle) {
diff --git a/src/utils/deconflictChunk.ts b/src/utils/deconflictChunk.ts
index d19c41dc2a3..96abb4973fb 100644
--- a/src/utils/deconflictChunk.ts
+++ b/src/utils/deconflictChunk.ts
@@ -15,21 +15,21 @@ import {
 import { getSafeName } from './safeName';
 
 export interface DependenciesToBeDeconflicted {
-	deconflictedDefault: Set<ExternalModule>;
-	deconflictedNamespace: Set<ExternalModule | Chunk>;
-	dependencies: Set<ExternalModule | Chunk>;
+	deconflictedDefault: ReadonlySet<ExternalModule>;
+	deconflictedNamespace: ReadonlySet<ExternalModule | Chunk>;
+	dependencies: ReadonlySet<ExternalModule | Chunk>;
 }
 
 const DECONFLICT_IMPORTED_VARIABLES_BY_FORMAT: {
 	[format in InternalModuleFormat]: (
 		usedNames: Set<string>,
-		imports: Set<Variable>,
+		imports: ReadonlySet<Variable>,
 		dependenciesToBeDeconflicted: DependenciesToBeDeconflicted,
 		interop: GetInterop,
 		preserveModules: boolean,
 		externalLiveBindings: boolean,
-		chunkByModule: Map<Module, Chunk>,
-		syntheticExports: Set<SyntheticNamedExportVariable>
+		chunkByModule: ReadonlyMap<Module, Chunk>,
+		syntheticExports: ReadonlySet<SyntheticNamedExportVariable>
 	) => void;
 } = {
 	amd: deconflictImportsOther,
@@ -43,16 +43,16 @@ const DECONFLICT_IMPORTED_VARIABLES_BY_FORMAT: {
 export function deconflictChunk(
 	modules: readonly Module[],
 	dependenciesToBeDeconflicted: DependenciesToBeDeconflicted,
-	imports: Set<Variable>,
+	imports: ReadonlySet<Variable>,
 	usedNames: Set<string>,
 	format: InternalModuleFormat,
 	interop: GetInterop,
 	preserveModules: boolean,
 	externalLiveBindings: boolean,
-	chunkByModule: Map<Module, Chunk>,
-	syntheticExports: Set<SyntheticNamedExportVariable>,
-	exportNamesByVariable: ReadonlyMap<Variable, string[]>,
-	accessedGlobalsByScope: ReadonlyMap<ChildScope, Set<string>>,
+	chunkByModule: ReadonlyMap<Module, Chunk>,
+	syntheticExports: ReadonlySet<SyntheticNamedExportVariable>,
+	exportNamesByVariable: ReadonlyMap<Variable, readonly string[]>,
+	accessedGlobalsByScope: ReadonlyMap<ChildScope, ReadonlySet<string>>,
 	includedNamespaces: ReadonlySet<Module>
 ): void {
 	const reversedModules = modules.slice().reverse();
@@ -88,8 +88,8 @@ function deconflictImportsEsmOrSystem(
 	_interop: GetInterop,
 	preserveModules: boolean,
 	_externalLiveBindings: boolean,
-	chunkByModule: Map<Module, Chunk>,
-	syntheticExports: Set<SyntheticNamedExportVariable>
+	chunkByModule: ReadonlyMap<Module, Chunk>,
+	syntheticExports: ReadonlySet<SyntheticNamedExportVariable>
 ) {
 	// This is needed for namespace reexports
 	for (const dependency of dependenciesToBeDeconflicted.dependencies) {
@@ -128,12 +128,12 @@ function deconflictImportsEsmOrSystem(
 
 function deconflictImportsOther(
 	usedNames: Set<string>,
-	imports: Set<Variable>,
+	imports: ReadonlySet<Variable>,
 	{ deconflictedDefault, deconflictedNamespace, dependencies }: DependenciesToBeDeconflicted,
 	interop: GetInterop,
 	preserveModules: boolean,
 	externalLiveBindings: boolean,
-	chunkByModule: Map<Module, Chunk>
+	chunkByModule: ReadonlyMap<Module, Chunk>
 ): void {
 	for (const chunkOrExternalModule of dependencies) {
 		chunkOrExternalModule.variableName = getSafeName(