diff --git a/crypto/dh/dh_lib.c b/crypto/dh/dh_lib.c
index bf9f8d3..644508d 100644
--- a/crypto/dh/dh_lib.c
+++ b/crypto/dh/dh_lib.c
@@ -245,15 +245,27 @@
 
 int DH_set0_pqg(DH *dh, BIGNUM *p, BIGNUM *q, BIGNUM *g)
 {
-    /* q is optional */
-    if (p == NULL || g == NULL)
+    /* If the fields p and g in d are NULL, the corresponding input
+     * parameters MUST be non-NULL.  q may remain NULL.
+     *
+     * It is an error to give the results from get0 on d
+     * as input parameters.
+     */
+    if (p == dh->p || (dh->q != NULL && q == dh->q) || g == dh->g)
         return 0;
-    BN_free(dh->p);
-    BN_free(dh->q);
-    BN_free(dh->g);
-    dh->p = p;
-    dh->q = q;
-    dh->g = g;
+
+    if (p != NULL) {
+        BN_free(dh->p);
+        dh->p = p;
+    }
+    if (q != NULL) {
+        BN_free(dh->q);
+        dh->q = q;
+    }
+    if (g != NULL) {
+        BN_free(dh->g);
+        dh->g = g;
+    }
 
     if (q != NULL) {
         dh->length = BN_num_bits(q);
@@ -283,14 +295,25 @@
 
 int DH_set0_key(DH *dh, BIGNUM *pub_key, BIGNUM *priv_key)
 {
-    /* Note that it is valid for priv_key to be NULL */
-    if (pub_key == NULL)
+    /* If the pub_key in dh is NULL, the corresponding input
+     * parameters MUST be non-NULL.  The priv_key field may
+     * be left NULL.
+     *
+     * It is an error to give the results from get0 on dh
+     * as input parameters.
+     */
+    if (dh->pub_key == pub_key
+        || (dh->priv_key != NULL && priv_key != dh->priv_key))
         return 0;
 
-    BN_free(dh->pub_key);
-    BN_free(dh->priv_key);
-    dh->pub_key = pub_key;
-    dh->priv_key = priv_key;
+    if (pub_key != NULL) {
+        BN_free(dh->pub_key);
+        dh->pub_key = pub_key;
+    }
+    if (priv_key != NULL) {
+        BN_free(dh->priv_key);
+        dh->priv_key = priv_key;
+    }
 
     return 1;
 }
diff --git a/crypto/dsa/dsa_lib.c b/crypto/dsa/dsa_lib.c
index facb97f..383b48b 100644
--- a/crypto/dsa/dsa_lib.c
+++ b/crypto/dsa/dsa_lib.c
@@ -315,14 +315,27 @@
 
 int DSA_set0_pqg(DSA *d, BIGNUM *p, BIGNUM *q, BIGNUM *g)
 {
-    if (p == NULL || q == NULL || g == NULL)
+    /* If the fields in d are NULL, the corresponding input
+     * parameters MUST be non-NULL.
+     *
+     * It is an error to give the results from get0 on d
+     * as input parameters.
+     */
+    if (p == d->p || q == d->q || g == d->g)
         return 0;
-    BN_free(d->p);
-    BN_free(d->q);
-    BN_free(d->g);
-    d->p = p;
-    d->q = q;
-    d->g = g;
+
+    if (p != NULL) {
+        BN_free(d->p);
+        d->p = p;
+    }
+    if (q != NULL) {
+        BN_free(d->q);
+        d->q = q;
+    }
+    if (g != NULL) {
+        BN_free(d->g);
+        d->g = g;
+    }
 
     return 1;
 }
@@ -337,14 +350,25 @@
 
 int DSA_set0_key(DSA *d, BIGNUM *pub_key, BIGNUM *priv_key)
 {
-    /* Note that it is valid for priv_key to be NULL */
-    if (pub_key == NULL)
+    /* If the pub_key in d is NULL, the corresponding input
+     * parameters MUST be non-NULL.  The priv_key field may
+     * be left NULL.
+     *
+     * It is an error to give the results from get0 on d
+     * as input parameters.
+     */
+    if (d->pub_key == pub_key
+        || (d->priv_key != NULL && priv_key != d->priv_key))
         return 0;
 
-    BN_free(d->pub_key);
-    BN_free(d->priv_key);
-    d->pub_key = pub_key;
-    d->priv_key = priv_key;
+    if (pub_key != NULL) {
+        BN_free(d->pub_key);
+        d->pub_key = pub_key;
+    }
+    if (priv_key != NULL) {
+        BN_free(d->priv_key);
+        d->priv_key = priv_key;
+    }
 
     return 1;
 }
diff --git a/crypto/rsa/rsa_lib.c b/crypto/rsa/rsa_lib.c
index 7ee575d..2226316 100644
--- a/crypto/rsa/rsa_lib.c
+++ b/crypto/rsa/rsa_lib.c
@@ -286,44 +286,79 @@
 
 int RSA_set0_key(RSA *r, BIGNUM *n, BIGNUM *e, BIGNUM *d)
 {
-    /* d is the private component and may be NULL */
-    if (n == NULL || e == NULL)
+    /* If the fields in r are NULL, the corresponding input
+     * parameters MUST be non-NULL for n and e.  d may be
+     * left NULL (in case only the public key is used).
+     *
+     * It is an error to give the results from get0 on r
+     * as input parameters.
+     */
+    if (n == r->n || e == r->e
+        || (r->d != NULL && d == r->d))
         return 0;
 
-    BN_free(r->n);
-    BN_free(r->e);
-    BN_free(r->d);
-    r->n = n;
-    r->e = e;
-    r->d = d;
+    if (n != NULL) {
+        BN_free(r->n);
+        r->n = n;
+    }
+    if (e != NULL) {
+        BN_free(r->e);
+        r->e = e;
+    }
+    if (d != NULL) {
+        BN_free(r->d);
+        r->d = d;
+    }
 
     return 1;
 }
 
 int RSA_set0_factors(RSA *r, BIGNUM *p, BIGNUM *q)
 {
-    if (p == NULL || q == NULL)
+    /* If the fields in r are NULL, the corresponding input
+     * parameters MUST be non-NULL.
+     *
+     * It is an error to give the results from get0 on r
+     * as input parameters.
+     */
+    if (p == r->p || q == r->q)
         return 0;
 
-    BN_free(r->p);
-    BN_free(r->q);
-    r->p = p;
-    r->q = q;
+    if (p != NULL) {
+        BN_free(r->p);
+        r->p = p;
+    }
+    if (q != NULL) {
+        BN_free(r->q);
+        r->q = q;
+    }
 
     return 1;
 }
 
 int RSA_set0_crt_params(RSA *r, BIGNUM *dmp1, BIGNUM *dmq1, BIGNUM *iqmp)
 {
-    if (dmp1 == NULL || dmq1 == NULL || iqmp == NULL)
+    /* If the fields in r are NULL, the corresponding input
+     * parameters MUST be non-NULL.
+     *
+     * It is an error to give the results from get0 on r
+     * as input parameters.
+     */
+    if (dmp1 == r->dmp1 || dmq1 == r->dmq1 || iqmp == r->iqmp)
         return 0;
 
-    BN_free(r->dmp1);
-    BN_free(r->dmq1);
-    BN_free(r->iqmp);
-    r->dmp1 = dmp1;
-    r->dmq1 = dmq1;
-    r->iqmp = iqmp;
+    if (dmp1 != NULL) {
+        BN_free(r->dmp1);
+        r->dmp1 = dmp1;
+    }
+    if (dmq1 != NULL) {
+        BN_free(r->dmq1);
+        r->dmq1 = dmq1;
+    }
+    if (iqmp != NULL) {
+        BN_free(r->iqmp);
+        r->iqmp = iqmp;
+    }
 
     return 1;
 }