diff --git a/lib/des/rsa.c b/lib/des/rsa.c
index aa4bbd6bf..496d8a8f2 100644
--- a/lib/des/rsa.c
+++ b/lib/des/rsa.c
@@ -379,6 +379,50 @@ d2i_RSAPrivateKey(RSA *rsa, const unsigned char **pp, size_t len)
     return k;
 }
 
+int
+i2d_RSAPrivateKey(RSA *rsa, unsigned char **pp)
+{
+    RSAPrivateKey data;
+    size_t size;
+    int ret;
+
+    memset(&data, 0, sizeof(data));
+
+    ret  = bn2heim_int(rsa->n, &data.modulus)
+    ret |= bn2heim_int(rsa->e, &data.publicExponent);
+    ret |= bn2heim_int(rsa->d, &data.privateExponent);
+    ret |= bn2heim_int(rsa->p, &data.prime1);
+    ret |= bn2heim_int(rsa->q, &data.prime2);
+    ret |= bn2heim_int(rsa->dmp1, &data.exponent1);
+    ret |= bn2heim_int(rsa->dmq1, &data.exponent2);
+    if (ret) {
+	free_RSAPrivateKey(&data);
+	return -1;
+    }
+
+    if (pp == NULL) {
+	size = length_RSAPrivateKey(&data);
+	free_RSAPrivateKey(&data);
+    } else {
+	void *p;
+	size_t len;
+
+	ASN1_MALLOC_ENCODE(RSAPrivateKey, p, len, &data, &size, ret);
+	free_RSAPrivateKey(&data);
+	if (ret)
+	    return -1;
+	if (len != size)
+	    abort();
+
+	memcpy(*pp, p, size);
+	free(p);
+
+	*pp += size;
+
+    }
+    return size;
+}
+
 int
 i2d_RSAPublicKey(RSA *rsa, unsigned char **pp)
 {
diff --git a/lib/des/rsa.h b/lib/des/rsa.h
index 58f8b8759..afc9818ce 100644
--- a/lib/des/rsa.h
+++ b/lib/des/rsa.h
@@ -61,6 +61,7 @@
 #define RSA_verify hc_RSA_verify
 #define RSA_generate_key_ex hc_RSA_generate_key_ex
 #define d2i_RSAPrivateKey hc_d2i_RSAPrivateKey
+#define i2d_RSAPrivateKey hc_i2d_RSAPrivateKey
 #define i2d_RSAPublicKey hc_i2d_RSAPublicKey
 
 /*
@@ -167,6 +168,8 @@ int RSA_verify(int, const unsigned char *, unsigned int,
 int	RSA_generate_key_ex(RSA *, int, BIGNUM *, BN_GENCB *);
 
 RSA *	d2i_RSAPrivateKey(RSA *, const unsigned char **, size_t);
+int	i2d_RSAPrivateKey(RSA *, unsigned char **);
+
 int	i2d_RSAPublicKey(RSA *, unsigned char **);
 
 #endif /* _HEIM_RSA_H */