diff --git a/CHANGES b/CHANGES
index 51e65b7743..6130aefff0 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1798,6 +1798,10 @@
      This fixes a DoS attack. (CVE-2013-0166)
      [Steve Henson]
 
+  *) Return an error when checking OCSP signatures when key is NULL.
+     This fixes a DoS attack. (CVE-2013-0166)
+     [Steve Henson]
+
   *) Call OCSP Stapling callback after ciphersuite has been chosen, so
      the right response is stapled. Also change SSL_get_certificate()
      so it returns the certificate actually sent.
diff --git a/crypto/asn1/a_verify.c b/crypto/asn1/a_verify.c
index 432722e409..fc84cd3d19 100644
--- a/crypto/asn1/a_verify.c
+++ b/crypto/asn1/a_verify.c
@@ -140,6 +140,12 @@ int ASN1_item_verify(const ASN1_ITEM *it, X509_ALGOR *a,
 
 	int mdnid, pknid;
 
+	if (!pkey)
+		{
+		ASN1err(ASN1_F_ASN1_ITEM_VERIFY, ERR_R_PASSED_NULL_PARAMETER);
+		return -1;
+		}
+
 	EVP_MD_CTX_init(&ctx);
 
 	/* Convert signature OID into digest and public key OIDs */
diff --git a/crypto/ocsp/ocsp_vfy.c b/crypto/ocsp/ocsp_vfy.c
index 8a5e788d96..276718304d 100644
--- a/crypto/ocsp/ocsp_vfy.c
+++ b/crypto/ocsp/ocsp_vfy.c
@@ -91,9 +91,12 @@ int OCSP_basic_verify(OCSP_BASICRESP *bs, STACK_OF(X509) *certs,
 		{
 		EVP_PKEY *skey;
 		skey = X509_get_pubkey(signer);
-		ret = OCSP_BASICRESP_verify(bs, skey, 0);
-		EVP_PKEY_free(skey);
-		if(ret <= 0)
+		if (skey)
+			{
+			ret = OCSP_BASICRESP_verify(bs, skey, 0);
+			EVP_PKEY_free(skey);
+			}
+		if(!skey || ret <= 0)
 			{
 			OCSPerr(OCSP_F_OCSP_BASIC_VERIFY, OCSP_R_SIGNATURE_FAILURE);
 			goto end;