diff --git a/folly/synchronization/test/FlatCombiningBenchmark.cpp b/folly/synchronization/test/FlatCombiningBenchmark.cpp
index f3263c85a..771414f4f 100644
--- a/folly/synchronization/test/FlatCombiningBenchmark.cpp
+++ b/folly/synchronization/test/FlatCombiningBenchmark.cpp
@@ -22,6 +22,8 @@
 
 using namespace folly::test;
 
+#include <iomanip>
+
 // use option --benchmark to run folly::Benchmark
 // use option --direct to run direct benchmark measurements
 DEFINE_bool(direct, false, "run direct measurement");