diff --git a/include/libssh/libmbedcrypto.h b/include/libssh/libmbedcrypto.h
index e6fc393cd31823288f61f56dc5929183ce27e9cf..6cf186261d1be88b70d98309fb4d6496a6ad0a59 100644
--- a/include/libssh/libmbedcrypto.h
+++ b/include/libssh/libmbedcrypto.h
@@ -79,7 +79,7 @@ extern "C" {
 
 bignum ssh_mbedcry_bn_new(void);
 void ssh_mbedcry_bn_free(bignum num);
-unsigned char *ssh_mbedcry_bn2num(const_bignum num, int radix);
+char *ssh_mbedcry_bn2num(const_bignum num, int radix);
 int ssh_mbedcry_rand(bignum rnd, int bits, int top, int bottom);
 int ssh_mbedcry_is_bit_set(bignum num, size_t pos);
 int ssh_mbedcry_rand_range(bignum dest, bignum max);
@@ -105,7 +105,7 @@ int ssh_mbedcry_hex2bn(bignum *dest, char *data);
     } while(0)
 #define bignum_bn2dec(num) ssh_mbedcry_bn2num(num, 10)
 #define bignum_dec2bn(data, bn) mbedtls_mpi_read_string(bn, 10, data)
-#define bignum_bn2hex(num, dest) (*dest)=ssh_mbedcry_bn2num(num, 16)
+#define bignum_bn2hex(num, dest) (*dest)=(unsigned char *)ssh_mbedcry_bn2num(num, 16)
 #define bignum_hex2bn(data, dest) ssh_mbedcry_hex2bn(dest, data)
 #define bignum_rand(rnd, bits) ssh_mbedcry_rand((rnd), (bits), 0, 1)
 #define bignum_rand_range(rnd, max) ssh_mbedcry_rand_range(rnd, max)
diff --git a/src/mbedcrypto_missing.c b/src/mbedcrypto_missing.c
index ac0d688c9bd206f4e1a798ea43a4c8884b28010a..fb35ca473ecd70a6e174917ac90a147c695da782 100644
--- a/src/mbedcrypto_missing.c
+++ b/src/mbedcrypto_missing.c
@@ -45,7 +45,7 @@ void ssh_mbedcry_bn_free(bignum bn)
     SAFE_FREE(bn);
 }
 
-unsigned char *ssh_mbedcry_bn2num(const_bignum num, int radix)
+char *ssh_mbedcry_bn2num(const_bignum num, int radix)
 {
     char *buf = NULL;
     size_t olen;
@@ -67,7 +67,7 @@ unsigned char *ssh_mbedcry_bn2num(const_bignum num, int radix)
         return NULL;
     }
 
-    return (unsigned char *) buf;
+    return buf;
 }
 
 int ssh_mbedcry_rand(bignum rnd, int bits, int top, int bottom)