diff --git a/include/secp256k1.h b/include/secp256k1.h
index fd6d6b1..a8ddf43 100644
--- a/include/secp256k1.h
+++ b/include/secp256k1.h
@@ -5,12 +5,16 @@
 extern "C" {
 #endif
 
+/** Flags to pass to secp256k1_start. */
+#define SECP256K1_START_VERIFY (1 << 0)
+#define SECP256K1_START_SIGN   (1 << 1)
+
 /** Initialize the library. This may take some time (10-100 ms).
  *  You need to call this before calling any other function.
  *  It cannot run in parallel with any other functions, but once
  *  secp256k1_start() returns, all other functions are thread-safe.
  */
-void secp256k1_start(void);
+void secp256k1_start(unsigned int flags);
 
 /** Free all memory associated with this library. After this, no
  *  functions can be called anymore, except secp256k1_start()
@@ -22,6 +26,7 @@ void secp256k1_stop(void);
  *           0: incorrect signature
  *          -1: invalid public key
  *          -2: invalid signature
+ * Requires starting using SECP256K1_START_VERIFY.
  */
 int secp256k1_ecdsa_verify(const unsigned char *msg, int msglen,
                            const unsigned char *sig, int siglen,
@@ -36,6 +41,7 @@ int secp256k1_ecdsa_verify(const unsigned char *msg, int msglen,
  *           nonce:  pointer to a 32-byte nonce (generated with a cryptographic PRNG)
  *  Out:     sig:    pointer to a 72-byte array where the signature will be placed.
  *           siglen: pointer to an int, which will be updated to the signature length (<=72).
+ * Requires starting using SECP256K1_START_SIGN.
  */
 int secp256k1_ecdsa_sign(const unsigned char *msg, int msglen,
                          unsigned char *sig, int *siglen,
@@ -51,6 +57,7 @@ int secp256k1_ecdsa_sign(const unsigned char *msg, int msglen,
  *           nonce:  pointer to a 32-byte nonce (generated with a cryptographic PRNG)
  *  Out:     sig:    pointer to a 64-byte array where the signature will be placed.
  *           recid:  pointer to an int, which will be updated to contain the recovery id.
+ * Requires starting using SECP256K1_START_SIGN.
  */
 int secp256k1_ecdsa_sign_compact(const unsigned char *msg, int msglen,
                                  unsigned char *sig64,
@@ -68,8 +75,8 @@ int secp256k1_ecdsa_sign_compact(const unsigned char *msg, int msglen,
  *           recid:      the recovery id (as returned by ecdsa_sign_compact)
  *  Out:     pubkey:     pointer to a 33 or 65 byte array to put the pubkey.
  *           pubkeylen:  pointer to an int that will contain the pubkey length.
+ * Requires starting using SECP256K1_START_VERIFY.
  */
-
 int secp256k1_ecdsa_recover_compact(const unsigned char *msg, int msglen,
                                     const unsigned char *sig64,
                                     unsigned char *pubkey, int *pubkeylen,
@@ -97,6 +104,7 @@ int secp256k1_ecdsa_pubkey_verify(const unsigned char *pubkey, int pubkeylen);
  *                      length.
  *  Returns: 1: secret was valid, public key stores
  *           0: secret was invalid, try again.
+ * Requires starting using SECP256K1_START_SIGN.
  */
 int secp256k1_ecdsa_pubkey_create(unsigned char *pubkey, int *pubkeylen, const unsigned char *seckey, int compressed);
 
diff --git a/src/ecmult_impl.h b/src/ecmult_impl.h
index b313b6c..c09cfec 100644
--- a/src/ecmult_impl.h
+++ b/src/ecmult_impl.h
@@ -69,7 +69,9 @@ typedef struct {
     // For accelerating the computation of a*P + b*G:
     secp256k1_ge_t pre_g[ECMULT_TABLE_SIZE(WINDOW_G)];    // odd multiples of the generator
     secp256k1_ge_t pre_g_128[ECMULT_TABLE_SIZE(WINDOW_G)]; // odd multiples of 2^128*generator
+} secp256k1_ecmult_consts_t;
 
+typedef struct {
     // For accelerating the computation of a*G:
     // To harden against timing attacks, use the following mechanism:
     // * Break up the multiplicand into groups of 4 bits, called n_0, n_1, n_2, ..., n_63.
@@ -83,9 +85,10 @@ typedef struct {
     // the intermediate sums while computing a*G.
     // To make memory access uniform, the bytes of prec(i, n_i) are sliced per value of n_i.
     unsigned char prec[64][sizeof(secp256k1_ge_t)][16]; // prec[j][k][i] = k'th byte of (16^j * i * G + U_i)
-} secp256k1_ecmult_consts_t;
+} secp256k1_ecmult_gen_consts_t;
 
 static const secp256k1_ecmult_consts_t *secp256k1_ecmult_consts = NULL;
+static const secp256k1_ecmult_gen_consts_t *secp256k1_ecmult_gen_consts = NULL;
 
 static void secp256k1_ecmult_start(void) {
     if (secp256k1_ecmult_consts != NULL)
@@ -106,6 +109,18 @@ static void secp256k1_ecmult_start(void) {
     // precompute the tables with odd multiples
     secp256k1_ecmult_table_precomp_ge(ret->pre_g, &gj, WINDOW_G);
     secp256k1_ecmult_table_precomp_ge(ret->pre_g_128, &g_128j, WINDOW_G);
+}
+
+static void secp256k1_ecmult_gen_start(void) {
+    if (secp256k1_ecmult_gen_consts != NULL)
+        return;
+
+    secp256k1_ecmult_gen_consts_t *ret = (secp256k1_ecmult_gen_consts_t*)malloc(sizeof(secp256k1_ecmult_gen_consts_t));
+    secp256k1_ecmult_gen_consts = ret;
+
+    // get the generator
+    const secp256k1_ge_t *g = &secp256k1_ge_consts->g;
+    secp256k1_gej_t gj; secp256k1_gej_set_ge(&gj, g);
 
     // Construct a group element with no known corresponding scalar (nothing up my sleeve).
     secp256k1_gej_t nums_gej;
@@ -165,6 +180,15 @@ static void secp256k1_ecmult_stop(void) {
     secp256k1_ecmult_consts = NULL;
 }
 
+static void secp256k1_ecmult_gen_stop(void) {
+    if (secp256k1_ecmult_gen_consts == NULL)
+        return;
+
+    secp256k1_ecmult_gen_consts_t *c = (secp256k1_ecmult_gen_consts_t*)secp256k1_ecmult_gen_consts;
+    free(c);
+    secp256k1_ecmult_gen_consts = NULL;
+}
+
 /** Convert a number to WNAF notation. The number becomes represented by sum(2^i * wnaf[i], i=0..bits),
  *  with the following guarantees:
  *  - each wnaf[i] is either 0, or an odd integer between -(1<<(w-1) - 1) and (1<<(w-1) - 1)
@@ -209,7 +233,7 @@ void static secp256k1_ecmult_gen(secp256k1_gej_t *r, const secp256k1_num_t *gn)
     secp256k1_num_t n;
     secp256k1_num_init(&n);
     secp256k1_num_copy(&n, gn);
-    const secp256k1_ecmult_consts_t *c = secp256k1_ecmult_consts;
+    const secp256k1_ecmult_gen_consts_t *c = secp256k1_ecmult_gen_consts;
     secp256k1_gej_set_infinity(r);
     secp256k1_ge_t add;
     int bits;
diff --git a/src/java/org_bitcoin_NativeSecp256k1.c b/src/java/org_bitcoin_NativeSecp256k1.c
index ed65ccc..bb4cd70 100644
--- a/src/java/org_bitcoin_NativeSecp256k1.c
+++ b/src/java/org_bitcoin_NativeSecp256k1.c
@@ -15,7 +15,7 @@ static void __javasecp256k1_attach(void) __attribute__((constructor));
 static void __javasecp256k1_detach(void) __attribute__((destructor));
 
 static void __javasecp256k1_attach(void) {
-	secp256k1_start();
+	secp256k1_start(SECP256K1_START_VERIFY);
 }
 
 static void __javasecp256k1_detach(void) {
diff --git a/src/secp256k1.c b/src/secp256k1.c
index 65ba146..1a6854e 100644
--- a/src/secp256k1.c
+++ b/src/secp256k1.c
@@ -2,6 +2,8 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include "include/secp256k1.h"
+
 #include <assert.h>
 #include "util.h"
 #include "num_impl.h"
@@ -10,19 +12,26 @@
 #include "ecmult_impl.h"
 #include "ecdsa_impl.h"
 
-void secp256k1_start(void) {
+void secp256k1_start(unsigned int flags) {
     secp256k1_fe_start();
     secp256k1_ge_start();
-    secp256k1_ecmult_start();
+    if (flags & SECP256K1_START_SIGN) {
+        secp256k1_ecmult_gen_start();
+    }
+    if (flags & SECP256K1_START_VERIFY) {
+        secp256k1_ecmult_start();
+    }
 }
 
 void secp256k1_stop(void) {
     secp256k1_ecmult_stop();
+    secp256k1_ecmult_gen_stop();
     secp256k1_ge_stop();
     secp256k1_fe_stop();
 }
 
 int secp256k1_ecdsa_verify(const unsigned char *msg, int msglen, const unsigned char *sig, int siglen, const unsigned char *pubkey, int pubkeylen) {
+    DEBUG_CHECK(secp256k1_ecmult_consts != NULL);
     DEBUG_CHECK(msg != NULL);
     DEBUG_CHECK(msglen <= 32);
     DEBUG_CHECK(sig != NULL);
@@ -56,6 +65,7 @@ end:
 }
 
 int secp256k1_ecdsa_sign(const unsigned char *message, int messagelen, unsigned char *signature, int *signaturelen, const unsigned char *seckey, const unsigned char *nonce) {
+    DEBUG_CHECK(secp256k1_ecmult_gen_consts != NULL);
     DEBUG_CHECK(message != NULL);
     DEBUG_CHECK(messagelen <= 32);
     DEBUG_CHECK(signature != NULL);
@@ -91,6 +101,7 @@ int secp256k1_ecdsa_sign(const unsigned char *message, int messagelen, unsigned
 }
 
 int secp256k1_ecdsa_sign_compact(const unsigned char *message, int messagelen, unsigned char *sig64, const unsigned char *seckey, const unsigned char *nonce, int *recid) {
+    DEBUG_CHECK(secp256k1_ecmult_gen_consts != NULL);
     DEBUG_CHECK(message != NULL);
     DEBUG_CHECK(messagelen <= 32);
     DEBUG_CHECK(sig64 != NULL);
@@ -126,6 +137,7 @@ int secp256k1_ecdsa_sign_compact(const unsigned char *message, int messagelen, u
 }
 
 int secp256k1_ecdsa_recover_compact(const unsigned char *msg, int msglen, const unsigned char *sig64, unsigned char *pubkey, int *pubkeylen, int compressed, int recid) {
+    DEBUG_CHECK(secp256k1_ecmult_consts != NULL);
     DEBUG_CHECK(msg != NULL);
     DEBUG_CHECK(msglen <= 32);
     DEBUG_CHECK(sig64 != NULL);
@@ -173,6 +185,7 @@ int secp256k1_ecdsa_pubkey_verify(const unsigned char *pubkey, int pubkeylen) {
 }
 
 int secp256k1_ecdsa_pubkey_create(unsigned char *pubkey, int *pubkeylen, const unsigned char *seckey, int compressed) {
+    DEBUG_CHECK(secp256k1_ecmult_gen_consts != NULL);
     DEBUG_CHECK(pubkey != NULL);
     DEBUG_CHECK(pubkeylen != NULL);
     DEBUG_CHECK(seckey != NULL);
@@ -230,6 +243,7 @@ int secp256k1_ecdsa_privkey_tweak_add(unsigned char *seckey, const unsigned char
 }
 
 int secp256k1_ecdsa_pubkey_tweak_add(unsigned char *pubkey, int pubkeylen, const unsigned char *tweak) {
+    DEBUG_CHECK(secp256k1_ecmult_consts != NULL);
     DEBUG_CHECK(pubkey != NULL);
     DEBUG_CHECK(tweak != NULL);
 
@@ -246,8 +260,12 @@ int secp256k1_ecdsa_pubkey_tweak_add(unsigned char *pubkey, int pubkeylen, const
     }
     if (ret) {
         secp256k1_gej_t pt;
-        secp256k1_ecmult_gen(&pt, &term);
-        secp256k1_gej_add_ge(&pt, &pt, &p);
+        secp256k1_gej_set_ge(&pt, &p);
+        secp256k1_num_t one;
+        secp256k1_num_init(&one);
+        secp256k1_num_set_int(&one, 1);
+        secp256k1_ecmult(&pt, &pt, &one, &term);
+        secp256k1_num_free(&one);
         if (secp256k1_gej_is_infinity(&pt))
             ret = 0;
         secp256k1_ge_set_gej(&p, &pt);
@@ -285,6 +303,7 @@ int secp256k1_ecdsa_privkey_tweak_mul(unsigned char *seckey, const unsigned char
 }
 
 int secp256k1_ecdsa_pubkey_tweak_mul(unsigned char *pubkey, int pubkeylen, const unsigned char *tweak) {
+    DEBUG_CHECK(secp256k1_ecmult_consts != NULL);
     DEBUG_CHECK(pubkey != NULL);
     DEBUG_CHECK(tweak != NULL);
 
diff --git a/src/tests.c b/src/tests.c
index b8f3c08..80ae0f4 100644
--- a/src/tests.c
+++ b/src/tests.c
@@ -704,7 +704,7 @@ int main(int argc, char **argv) {
     printf("test count = %i\n", count);
 
     // initialize
-    secp256k1_start();
+    secp256k1_start(SECP256K1_START_SIGN | SECP256K1_START_VERIFY);
 
     // num tests
     run_num_smalltests();