diff --git a/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts b/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
index b7a7c7017d0..c43140980b6 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
@@ -141,7 +141,7 @@ export class MainThreadDebugService implements MainThreadDebugServiceShape, IDeb
 		return void 0;
 	}
 
-	private convertToDto(bps: (IBreakpoint | IFunctionBreakpoint)[]): (ISourceBreakpointDto | IFunctionBreakpointDto)[] {
+	private convertToDto(bps: (ReadonlyArray<IBreakpoint | IFunctionBreakpoint>)): (ISourceBreakpointDto | IFunctionBreakpointDto)[] {
 		return bps.map(bp => {
 			if ('name' in bp) {
 				const fbp = <IFunctionBreakpoint>bp;
diff --git a/src/vs/workbench/parts/debug/browser/breakpointsView.ts b/src/vs/workbench/parts/debug/browser/breakpointsView.ts
index f1413ed1e93..a4d5380cde6 100644
--- a/src/vs/workbench/parts/debug/browser/breakpointsView.ts
+++ b/src/vs/workbench/parts/debug/browser/breakpointsView.ts
@@ -202,7 +202,7 @@ export class BreakpointsView extends ViewsViewletPanel {
 
 	private get elements(): IEnablement[] {
 		const model = this.debugService.getModel();
-		const elements = (<IEnablement[]>model.getExceptionBreakpoints()).concat(model.getFunctionBreakpoints()).concat(model.getBreakpoints());
+		const elements = (<ReadonlyArray<IEnablement>>model.getExceptionBreakpoints()).concat(model.getFunctionBreakpoints()).concat(model.getBreakpoints());
 
 		return elements;
 	}
diff --git a/src/vs/workbench/parts/debug/browser/debugActions.ts b/src/vs/workbench/parts/debug/browser/debugActions.ts
index 529dde3128c..5b4232955dc 100644
--- a/src/vs/workbench/parts/debug/browser/debugActions.ts
+++ b/src/vs/workbench/parts/debug/browser/debugActions.ts
@@ -453,7 +453,7 @@ export class EnableAllBreakpointsAction extends AbstractDebugAction {
 
 	protected isEnabled(state: State): boolean {
 		const model = this.debugService.getModel();
-		return super.isEnabled(state) && (<IEnablement[]>model.getBreakpoints()).concat(model.getFunctionBreakpoints()).concat(model.getExceptionBreakpoints()).some(bp => !bp.enabled);
+		return super.isEnabled(state) && (<ReadonlyArray<IEnablement>>model.getBreakpoints()).concat(model.getFunctionBreakpoints()).concat(model.getExceptionBreakpoints()).some(bp => !bp.enabled);
 	}
 }
 
@@ -472,7 +472,7 @@ export class DisableAllBreakpointsAction extends AbstractDebugAction {
 
 	protected isEnabled(state: State): boolean {
 		const model = this.debugService.getModel();
-		return super.isEnabled(state) && (<IEnablement[]>model.getBreakpoints()).concat(model.getFunctionBreakpoints()).concat(model.getExceptionBreakpoints()).some(bp => bp.enabled);
+		return super.isEnabled(state) && (<ReadonlyArray<IEnablement>>model.getBreakpoints()).concat(model.getFunctionBreakpoints()).concat(model.getExceptionBreakpoints()).some(bp => bp.enabled);
 	}
 }
 
diff --git a/src/vs/workbench/parts/debug/common/debug.ts b/src/vs/workbench/parts/debug/common/debug.ts
index bc9a8c933fb..1909b03c8e9 100644
--- a/src/vs/workbench/parts/debug/common/debug.ts
+++ b/src/vs/workbench/parts/debug/common/debug.ts
@@ -306,13 +306,13 @@ export interface IViewModel extends ITreeElement {
 }
 
 export interface IModel extends ITreeElement {
-	getProcesses(): IProcess[];
-	getBreakpoints(): IBreakpoint[];
+	getProcesses(): ReadonlyArray<IProcess>;
+	getBreakpoints(): ReadonlyArray<IBreakpoint>;
 	areBreakpointsActivated(): boolean;
-	getFunctionBreakpoints(): IFunctionBreakpoint[];
-	getExceptionBreakpoints(): IExceptionBreakpoint[];
-	getWatchExpressions(): IExpression[];
-	getReplElements(): IReplElement[];
+	getFunctionBreakpoints(): ReadonlyArray<IFunctionBreakpoint>;
+	getExceptionBreakpoints(): ReadonlyArray<IExceptionBreakpoint>;
+	getWatchExpressions(): ReadonlyArray<IExpression>;
+	getReplElements(): ReadonlyArray<IReplElement>;
 
 	onDidChangeBreakpoints: Event<IBreakpointsChangeEvent>;
 	onDidChangeCallStack: Event<void>;