diff --git a/src/crypto/crypto_util.h b/src/crypto/crypto_util.h
index c9f8c62a8d034f..82e970bb818a1d 100644
--- a/src/crypto/crypto_util.h
+++ b/src/crypto/crypto_util.h
@@ -22,6 +22,8 @@
 #ifndef OPENSSL_NO_ENGINE
 #  include <openssl/engine.h>
 #endif  // !OPENSSL_NO_ENGINE
+// The FIPS-related functions are only available
+// when the OpenSSL itself was compiled with FIPS support.
 #ifdef  OPENSSL_FIPS
 #  include <openssl/fips.h>
 #endif  // OPENSSL_FIPS