diff --git a/crypto/x509/x509_vfy.c b/crypto/x509/x509_vfy.c
index 33896fbc6..a2f1dbefe 100644
--- a/crypto/x509/x509_vfy.c
+++ b/crypto/x509/x509_vfy.c
@@ -198,6 +198,14 @@ int X509_verify_cert(X509_STORE_CTX *ctx)
         X509err(X509_F_X509_VERIFY_CERT, X509_R_NO_CERT_SET_FOR_US_TO_VERIFY);
         return -1;
     }
+    if (ctx->chain != NULL) {
+        /*
+         * This X509_STORE_CTX has already been used to verify a cert. We
+         * cannot do another one.
+         */
+        X509err(X509_F_X509_VERIFY_CERT, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
+        return -1;
+    }
 
     cb = ctx->verify_cb;
 
@@ -205,15 +213,13 @@ int X509_verify_cert(X509_STORE_CTX *ctx)
      * first we make sure the chain we are going to build is present and that
      * the first entry is in place
      */
-    if (ctx->chain == NULL) {
-        if (((ctx->chain = sk_X509_new_null()) == NULL) ||
-            (!sk_X509_push(ctx->chain, ctx->cert))) {
-            X509err(X509_F_X509_VERIFY_CERT, ERR_R_MALLOC_FAILURE);
-            goto end;
-        }
-        CRYPTO_add(&ctx->cert->references, 1, CRYPTO_LOCK_X509);
-        ctx->last_untrusted = 1;
+    if (((ctx->chain = sk_X509_new_null()) == NULL) ||
+        (!sk_X509_push(ctx->chain, ctx->cert))) {
+        X509err(X509_F_X509_VERIFY_CERT, ERR_R_MALLOC_FAILURE);
+        goto end;
     }
+    CRYPTO_add(&ctx->cert->references, 1, CRYPTO_LOCK_X509);
+    ctx->last_untrusted = 1;
 
     /* We use a temporary STACK so we can chop and hack at it */
     if (ctx->untrusted != NULL
diff --git a/doc/crypto/X509_STORE_CTX_new.pod b/doc/crypto/X509_STORE_CTX_new.pod
index b17888f14..eb38b0a10 100644
--- a/doc/crypto/X509_STORE_CTX_new.pod
+++ b/doc/crypto/X509_STORE_CTX_new.pod
@@ -39,10 +39,15 @@ X509_STORE_CTX_free() completely frees up B<ctx>. After this call B<ctx>
 is no longer valid.
 
 X509_STORE_CTX_init() sets up B<ctx> for a subsequent verification operation.
-The trusted certificate store is set to B<store>, the end entity certificate
-to be verified is set to B<x509> and a set of additional certificates (which
-will be untrusted but may be used to build the chain) in B<chain>. Any or
-all of the B<store>, B<x509> and B<chain> parameters can be B<NULL>.
+It must be called before each call to X509_verify_cert(), i.e. a B<ctx> is only
+good for one call to X509_verify_cert(); if you want to verify a second
+certificate with the same B<ctx> then you must call X509_XTORE_CTX_cleanup()
+and then X509_STORE_CTX_init() again before the second call to
+X509_verify_cert(). The trusted certificate store is set to B<store>, the end
+entity certificate to be verified is set to B<x509> and a set of additional
+certificates (which will be untrusted but may be used to build the chain) in
+B<chain>. Any or all of the B<store>, B<x509> and B<chain> parameters can be
+B<NULL>.
 
 X509_STORE_CTX_trusted_stack() sets the set of trusted certificates of B<ctx>
 to B<sk>. This is an alternative way of specifying trusted certificates 
diff --git a/doc/crypto/X509_verify_cert.pod b/doc/crypto/X509_verify_cert.pod
index 5253bdcd7..a22e44118 100644
--- a/doc/crypto/X509_verify_cert.pod
+++ b/doc/crypto/X509_verify_cert.pod
@@ -32,7 +32,8 @@ OpenSSL internally for certificate validation, in both the S/MIME and
 SSL/TLS code.
 
 The negative return value from X509_verify_cert() can only occur if no
-certificate is set in B<ctx> (due to a programming error) or if a retry
+certificate is set in B<ctx> (due to a programming error); if X509_verify_cert()
+twice without reinitialising B<ctx> in between; or if a retry
 operation is requested during internal lookups (which never happens with
 standard lookup methods). It is however recommended that application check
 for <= 0 return value on error.