diff --git a/truncate/benchmark/benchmark.js b/truncate/benchmark/benchmark.js
index 175d1c7f..e2838175 100644
--- a/truncate/benchmark/benchmark.js
+++ b/truncate/benchmark/benchmark.js
@@ -57,7 +57,7 @@ function createBenchmark( len ) {
 			}
 		}
 		b.toc();
-		if ( typeof out !== 'string' ) {
+		if ( !isString( out ) ) {
 			b.fail( 'should return a string' );
 		}
 		b.pass( 'benchmark finished' );