diff --git a/packages/core/src/browser/preferences/preference-service.ts b/packages/core/src/browser/preferences/preference-service.ts
index cbaf9e683d570..381c44dc72a47 100644
--- a/packages/core/src/browser/preferences/preference-service.ts
+++ b/packages/core/src/browser/preferences/preference-service.ts
@@ -70,7 +70,7 @@ export interface PreferenceService extends Disposable {
     readonly ready: Promise<void>;
     get<T>(preferenceName: string): T | undefined;
     get<T>(preferenceName: string, defaultValue: T): T;
-    get<T>(preferenceName: string, defaultValue: T, resourceUri: string): T;
+    get<T>(preferenceName: string, defaultValue: T, resourceUri?: string): T;
     get<T>(preferenceName: string, defaultValue?: T, resourceUri?: string): T | undefined;
     set(preferenceName: string, value: any, scope?: PreferenceScope, resourceUri?: string): Promise<void>;
     onPreferenceChanged: Event<PreferenceChange>;
diff --git a/packages/preferences/src/browser/abstract-resource-preference-provider.ts b/packages/preferences/src/browser/abstract-resource-preference-provider.ts
index d73c5ea13dc79..85a0a78aac244 100644
--- a/packages/preferences/src/browser/abstract-resource-preference-provider.ts
+++ b/packages/preferences/src/browser/abstract-resource-preference-provider.ts
@@ -20,7 +20,7 @@ import * as jsoncparser from 'jsonc-parser';
 import { JSONExt } from '@phosphor/coreutils/lib/json';
 import { inject, injectable, postConstruct } from 'inversify';
 import { MessageService, Resource, ResourceProvider, Disposable } from '@theia/core';
-import { PreferenceProvider, PreferenceSchemaProvider, PreferenceScope, PreferenceProviderDataChange } from '@theia/core/lib/browser';
+import { PreferenceProvider, PreferenceSchemaProvider, PreferenceScope, PreferenceProviderDataChange, PreferenceService } from '@theia/core/lib/browser';
 import URI from '@theia/core/lib/common/uri';
 import { PreferenceConfigurations } from '@theia/core/lib/browser/preferences/preference-configurations';
 
@@ -30,6 +30,7 @@ export abstract class AbstractResourcePreferenceProvider extends PreferenceProvi
     protected preferences: { [key: string]: any } = {};
     protected resource: Promise<Resource>;
 
+    @inject(PreferenceService) protected readonly preferenceService: PreferenceService;
     @inject(ResourceProvider) protected readonly resourceProvider: ResourceProvider;
     @inject(MessageService) protected readonly messageService: MessageService;
     @inject(PreferenceSchemaProvider) protected readonly schemaProvider: PreferenceSchemaProvider;
@@ -104,7 +105,8 @@ export abstract class AbstractResourcePreferenceProvider extends PreferenceProvi
         try {
             let newContent = '';
             if (path.length || value !== undefined) {
-                const formattingOptions = { tabSize: 3, insertSpaces: true, eol: '' };
+                const [tabSize, insertSpaces] = this.getFormattingOptions(resourceUri);
+                const formattingOptions = { tabSize, insertSpaces, eol: '' };
                 const edits = jsoncparser.modify(content, path, value, { formattingOptions });
                 newContent = jsoncparser.applyEdits(content, edits);
             }
@@ -221,4 +223,21 @@ export abstract class AbstractResourcePreferenceProvider extends PreferenceProvi
         }
     }
 
+    /**
+     * Get the formatting options to be used when calling `jsoncparser`.
+     * The formatting options are based on the corresponding preference values.
+     * @param uri the preference settings URI.
+     *
+     * @returns a tuple representing the tab indentation size, and if it is spaces.
+     */
+    protected getFormattingOptions(uri?: string): [number, boolean] {
+        console.log(`spaces?: ${this.preferenceService.get('[json].editor.insertSpaces', undefined, uri)}`);
+        return [
+            // Get the preference value for `tabSize`. Defaults to 2 if undefined.
+            this.preferenceService.get('[json].editor.tabSize', 2, uri),
+            // Get the preference value for `insertSpaces`. Defaults to `true` if undefined.
+            this.preferenceService.get('[json].editor.insertSpaces', true, uri)
+        ];
+    }
+
 }