diff --git a/CHANGES b/CHANGES
index 4169725bd..4571e7434 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,10 @@
 
  Changes between 0.9.6 and 0.9.6a  [xx XXX 2000]
 
+  *) Increase BN_CTX_NUM (the number of BIGNUMs in a BN_CTX) to 16.
+     The previous value, 12, was not always sufficient for BN_mod_exp().
+     [Bodo Moeller]
+
   *) Fix typo in get_cert_by_subject() in by_dir.c
      [Jean-Marc Desperrier <jean-marc.desperrier@certplus.com>]
 
diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h
index 1eb8395b2..3f6864fcf 100644
--- a/crypto/bn/bn.h
+++ b/crypto/bn/bn.h
@@ -239,7 +239,7 @@ typedef struct bignum_st
 	} BIGNUM;
 
 /* Used for temp variables */
-#define BN_CTX_NUM	12
+#define BN_CTX_NUM	16
 #define BN_CTX_NUM_POS	12
 typedef struct bignum_ctx
 	{
diff --git a/crypto/bn/bn_div.c b/crypto/bn/bn_div.c
index c3772c243..3b997087b 100644
--- a/crypto/bn/bn_div.c
+++ b/crypto/bn/bn_div.c
@@ -180,13 +180,13 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 
 	BN_CTX_start(ctx);
 	tmp=BN_CTX_get(ctx);
-	tmp->neg=0;
 	snum=BN_CTX_get(ctx);
 	sdiv=BN_CTX_get(ctx);
 	if (dv == NULL)
 		res=BN_CTX_get(ctx);
 	else	res=dv;
-	if (res == NULL) goto err;
+	if (sdiv==NULL || res == NULL) goto err;
+	tmp->neg=0;
 
 	/* First we normalise the numbers */
 	norm_shift=BN_BITS2-((BN_num_bits(divisor))%BN_BITS2);