diff --git a/lib/reporters/json.js b/lib/reporters/json.js
index 6194d8747d..2ea4ed913b 100644
--- a/lib/reporters/json.js
+++ b/lib/reporters/json.js
@@ -78,7 +78,16 @@ function JSONReporter(runner, options = {}) {
 
     runner.testResults = obj;
 
-    var json = JSON.stringify(obj, null, 2);
+    var optionsIndentSize;
+    if (options.reporterOption && 'indentSize' in options.reporterOption) {
+      optionsIndentSize = options.reporterOption.indentSize;
+    } else {
+      optionsIndentSize = 2; // Default Indentation size
+    }
+
+    var indentSize = parseInt(optionsIndentSize, 10); // Cast string to int
+
+    var json = JSON.stringify(obj, null, indentSize);
     if (output) {
       try {
         fs.mkdirSync(path.dirname(output), {recursive: true});