diff --git a/src/cdk/coercion/array.ts b/src/cdk/coercion/array.ts
index 6ab9c7eb1d4b..ca2d7104e1d0 100644
--- a/src/cdk/coercion/array.ts
+++ b/src/cdk/coercion/array.ts
@@ -7,6 +7,6 @@
  */
 
 /** Wraps the provided value in an array, unless the provided value is an array. */
-export function coerceArray<T>(value: T | T[]): T[] {
+export function coerceArray<T>(value: T | readonly T[]): T[] {
   return Array.isArray(value) ? value : [value];
 }
diff --git a/tools/public_api_guard/cdk/coercion.d.ts b/tools/public_api_guard/cdk/coercion.d.ts
index 1cf0d8e786ec..4cba9b987ecb 100644
--- a/tools/public_api_guard/cdk/coercion.d.ts
+++ b/tools/public_api_guard/cdk/coercion.d.ts
@@ -2,7 +2,7 @@ export declare function _isNumberValue(value: any): boolean;
 
 export declare type BooleanInput = string | boolean | null | undefined;
 
-export declare function coerceArray<T>(value: T | T[]): T[];
+export declare function coerceArray<T>(value: T | readonly T[]): T[];
 
 export declare function coerceBooleanProperty(value: any): boolean;