diff --git a/include/openssl/bn.h b/include/openssl/bn.h
index c895cc1..c198f4d 100644
--- a/include/openssl/bn.h
+++ b/include/openssl/bn.h
@@ -160,7 +160,7 @@
 #define BN_DEC_FMT1 "%" PRIu32
 #define BN_DEC_FMT2 "%09" PRIu32
 #define BN_HEX_FMT1 "%" PRIx32
-#define BN_HEX_FMT2 "%08" PRIx64
+#define BN_HEX_FMT2 "%08" PRIx32
 #else
 #error "Must define either OPENSSL_32_BIT or OPENSSL_64_BIT"
 #endif