diff --git a/test/content/runtests.js b/test/content/runtests.js
index 4c7b6b05cb..ac642a986a 100644
--- a/test/content/runtests.js
+++ b/test/content/runtests.js
@@ -141,9 +141,9 @@ function Reporter(runner) {
 		let indentStr = indent();
 		dump("\r" + indentStr
 			// Dark red X for errors
-			+ "\033[31;40m" + Mocha.reporters.Base.symbols.err + " [FAIL]\033[0m"
+			+ "\x1B[31;40m" + Mocha.reporters.Base.symbols.err + " [FAIL]\x1B[0m"
 			// Trigger bell if interactive
-			+ (Zotero.automatedTest ? "" : "\007")
+			+ (Zotero.automatedTest ? "" : "\x07")
 			+ " " + test.title + "\n"
 			+ indentStr + "  " + err.toString() + " at\n"
 			+ err.stack.replace(/^/gm, indentStr + "    "));