diff --git a/crypto/dh/dh_check.c b/crypto/dh/dh_check.c
index d85696b462..3f9e90e924 100644
--- a/crypto/dh/dh_check.c
+++ b/crypto/dh/dh_check.c
@@ -142,22 +142,38 @@ int DH_check(const DH *dh, int *ret)
 int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
 {
     int ok = 0;
-    BIGNUM *q = NULL;
+    BIGNUM *tmp = NULL;
+    BN_CTX *ctx = NULL;
 
     *ret = 0;
-    q = BN_new();
-    if (q == NULL)
+    ctx = BN_CTX_new();
+    if (ctx == NULL)
         goto err;
-    BN_set_word(q, 1);
-    if (BN_cmp(pub_key, q) <= 0)
+    BN_CTX_start(ctx);
+    tmp = BN_CTX_get(ctx);
+    if (tmp == NULL)
+        goto err;
+    BN_set_word(tmp, 1);
+    if (BN_cmp(pub_key, tmp) <= 0)
         *ret |= DH_CHECK_PUBKEY_TOO_SMALL;
-    BN_copy(q, dh->p);
-    BN_sub_word(q, 1);
-    if (BN_cmp(pub_key, q) >= 0)
+    BN_copy(tmp, dh->p);
+    BN_sub_word(tmp, 1);
+    if (BN_cmp(pub_key, tmp) >= 0)
         *ret |= DH_CHECK_PUBKEY_TOO_LARGE;
 
+    if (dh->q != NULL) {
+        /* Check pub_key^q == 1 mod p */
+        if (!BN_mod_exp(tmp, pub_key, dh->q, dh->p, ctx))
+            goto err;
+        if (!BN_is_one(tmp))
+            *ret |= DH_CHECK_PUBKEY_INVALID;
+    }
+
     ok = 1;
  err:
-    BN_free(q);
+    if (ctx != NULL) {
+        BN_CTX_end(ctx);
+        BN_CTX_free(ctx);
+    }
     return (ok);
 }
diff --git a/include/openssl/dh.h b/include/openssl/dh.h
index 528f52794d..90cfb82d85 100644
--- a/include/openssl/dh.h
+++ b/include/openssl/dh.h
@@ -174,6 +174,7 @@ struct dh_st {
 /* DH_check_pub_key error codes */
 # define DH_CHECK_PUBKEY_TOO_SMALL       0x01
 # define DH_CHECK_PUBKEY_TOO_LARGE       0x02
+# define DH_CHECK_PUBKEY_INVALID         0x03
 
 /*
  * primes p where (p-1)/2 is prime too are called "safe"; we define this for