diff --git a/dpf/aes_128_fixed_key_hash.cc b/dpf/aes_128_fixed_key_hash.cc
index 6300457..f7df231 100644
--- a/dpf/aes_128_fixed_key_hash.cc
+++ b/dpf/aes_128_fixed_key_hash.cc
@@ -26,6 +26,7 @@
 #include "absl/numeric/int128.h"
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
+#include "absl/strings/str_cat.h"
 #include "absl/types/span.h"
 #include "openssl/err.h"