diff --git a/lib/hcrypto/dh.c b/lib/hcrypto/dh.c
index 769934752..3ad37f87a 100644
--- a/lib/hcrypto/dh.c
+++ b/lib/hcrypto/dh.c
@@ -513,7 +513,7 @@ bn2heim_int(BIGNUM *bn, heim_integer *integer)
  */
 
 int
-i2d_DHparams(DH *dh, const char **pp)
+i2d_DHparams(DH *dh, unsigned char **pp)
 {
     DHParameter data;
     size_t size;
diff --git a/lib/hcrypto/dh.h b/lib/hcrypto/dh.h
index d4c2a0397..7c827df36 100644
--- a/lib/hcrypto/dh.h
+++ b/lib/hcrypto/dh.h
@@ -140,7 +140,7 @@ int	DH_check_pubkey(const DH *, const BIGNUM *, int *);
 int	DH_generate_key(DH *);
 int	DH_compute_key(unsigned char *,const BIGNUM *,DH *);
 
-int	i2d_DHparams(DH *, const char **);
+int	i2d_DHparams(DH *, unsigned char **);
 
 #endif /* _HEIM_DH_H */