diff --git a/crypto/bn/rsaz_exp.h b/crypto/bn/rsaz_exp.h
index 1c5e6188bc226eeaeb2c60d7b8c587479e06ed07..488b136f2c065d19d4225f50b8c842e426bae678 100644
--- a/crypto/bn/rsaz_exp.h
+++ b/crypto/bn/rsaz_exp.h
@@ -28,7 +28,7 @@ void RSAZ_1024_mod_exp_avx2(BN_ULONG result[16],
                             const BN_ULONG exponent[16],
                             const BN_ULONG m_norm[16], const BN_ULONG RR[16],
                             BN_ULONG k0);
-int rsaz_avx2_eligible();
+int rsaz_avx2_eligible(void);
 
 void RSAZ_512_mod_exp(BN_ULONG result[8],
                       const BN_ULONG base_norm[8], const BN_ULONG exponent[8],