diff --git a/cube.c b/cube.c
index d2ef882..33ef6d3 100644
--- a/cube.c
+++ b/cube.c
@@ -589,7 +589,8 @@ static void classify_grid_square_callback(void *ctx, struct grid_square *sq)
 	data->squareindex++;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     struct grid_data data;
     int i, j, k, m, area, facesperclass;
@@ -690,6 +691,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return seed;
 }
 
+static void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static void add_grid_square_callback(void *ctx, struct grid_square *sq)
 {
     game_state *state = (game_state *)ctx;
@@ -1546,6 +1552,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/fifteen.c b/fifteen.c
index 8439faa..e31843d 100644
--- a/fifteen.c
+++ b/fifteen.c
@@ -152,7 +152,8 @@ static int perm_parity(int *perm, int n)
     return ret;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     int gap, n, i, x;
     int x1, x2, p1, p2, parity;
@@ -267,6 +268,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return ret;
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     char *p, *err;
@@ -776,6 +782,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/gtk.c b/gtk.c
index 8c6a634..66ee767 100644
--- a/gtk.c
+++ b/gtk.c
@@ -1203,9 +1203,12 @@ int main(int argc, char **argv)
 	parstr = thegame.encode_params(par);
 
 	while (n-- > 0) {
-	    char *seed = thegame.new_seed(par, rs);
+	    game_aux_info *aux = NULL;
+	    char *seed = thegame.new_seed(par, rs, &aux);
 	    printf("%s:%s\n", parstr, seed);
 	    sfree(seed);
+	    if (aux)
+		thegame.free_aux_info(aux);
 	}
 
 	return 0;
diff --git a/midend.c b/midend.c
index efe8111..dbbaad4 100644
--- a/midend.c
+++ b/midend.c
@@ -17,6 +17,7 @@ struct midend_data {
     const game *ourgame;
 
     char *seed;
+    game_aux_info *aux_info;
     int fresh_seed;
     int nstates, statesize, statepos;
 
@@ -58,6 +59,7 @@ midend_data *midend_new(frontend *fe, const game *ourgame)
     me->states = NULL;
     me->params = ourgame->default_params();
     me->seed = NULL;
+    me->aux_info = NULL;
     me->fresh_seed = FALSE;
     me->drawstate = NULL;
     me->oldstate = NULL;
@@ -79,6 +81,8 @@ void midend_free(midend_data *me)
 {
     sfree(me->states);
     sfree(me->seed);
+    if (me->aux_info)
+	me->ourgame->free_aux_info(me->aux_info);
     me->ourgame->free_params(me->params);
     sfree(me);
 }
@@ -106,7 +110,11 @@ void midend_new_game(midend_data *me)
 
     if (!me->fresh_seed) {
 	sfree(me->seed);
-	me->seed = me->ourgame->new_seed(me->params, me->random);
+	if (me->aux_info)
+	    me->ourgame->free_aux_info(me->aux_info);
+	me->aux_info = NULL;
+	me->seed = me->ourgame->new_seed(me->params, me->random,
+					 &me->aux_info);
     } else
 	me->fresh_seed = FALSE;
 
@@ -399,9 +407,12 @@ float *midend_colours(midend_data *me, int *ncolours)
     float *ret;
 
     if (me->nstates == 0) {
-        char *seed = me->ourgame->new_seed(me->params, me->random);
+	game_aux_info *aux = NULL;
+        char *seed = me->ourgame->new_seed(me->params, me->random, &aux);
         state = me->ourgame->new_game(me->params, seed);
         sfree(seed);
+	if (aux)
+	    me->ourgame->free_aux_info(aux);
     } else
         state = me->states[0];
 
@@ -540,6 +551,9 @@ char *midend_game_id(midend_data *me, char *id, int def_seed)
         sfree(me->seed);
         me->seed = dupstr(seed);
         me->fresh_seed = TRUE;
+	if (me->aux_info)
+	    me->ourgame->free_aux_info(me->aux_info);
+	me->aux_info = NULL;
     }
 
     return NULL;
diff --git a/net.c b/net.c
index 78df30d..3d4daa7 100644
--- a/net.c
+++ b/net.c
@@ -290,7 +290,8 @@ static char *validate_params(game_params *params)
  * Randomly select a new game seed.
  */
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     /*
      * The full description of a Net game is far too large to
@@ -308,6 +309,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return dupstr(buf);
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     /*
@@ -1509,6 +1515,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/netslide.c b/netslide.c
index 11ca2ef..a7c3292 100644
--- a/netslide.c
+++ b/netslide.c
@@ -308,7 +308,8 @@ static char *validate_params(game_params *params)
  * Randomly select a new game seed.
  */
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     /*
      * The full description of a Net game is far too large to
@@ -326,6 +327,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return dupstr(buf);
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     /*
@@ -1533,6 +1539,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/nullgame.c b/nullgame.c
index 9e2ea32..296e76e 100644
--- a/nullgame.c
+++ b/nullgame.c
@@ -88,11 +88,17 @@ static char *validate_params(game_params *params)
     return NULL;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     return dupstr("FIXME");
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     return NULL;
@@ -223,6 +229,7 @@ const struct game thegame = {
     FALSE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/pattern.c b/pattern.c
index 6dda1f4..55f840f 100644
--- a/pattern.c
+++ b/pattern.c
@@ -476,7 +476,8 @@ static unsigned char *generate_soluble(random_state *rs, int w, int h)
     return grid;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     unsigned char *grid;
     int i, j, max, rowlen, *rowdata;
@@ -540,6 +541,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return seed;
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     int i, n, rowspace;
@@ -1030,6 +1036,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/puzzles.h b/puzzles.h
index d5c8924..1a4f10f 100644
--- a/puzzles.h
+++ b/puzzles.h
@@ -52,6 +52,7 @@ typedef struct midend_data midend_data;
 typedef struct random_state random_state;
 typedef struct game_params game_params;
 typedef struct game_state game_state;
+typedef struct game_aux_info game_aux_info;
 typedef struct game_ui game_ui;
 typedef struct game_drawstate game_drawstate;
 typedef struct game game;
@@ -189,7 +190,9 @@ struct game {
     config_item *(*configure)(game_params *params);
     game_params *(*custom_params)(config_item *cfg);
     char *(*validate_params)(game_params *params);
-    char *(*new_seed)(game_params *params, random_state *rs);
+    char *(*new_seed)(game_params *params, random_state *rs,
+		      game_aux_info **aux);
+    void (*free_aux_info)(game_aux_info *aux);
     char *(*validate_seed)(game_params *params, char *seed);
     game_state *(*new_game)(game_params *params, char *seed);
     game_state *(*dup_game)(game_state *state);
diff --git a/rect.c b/rect.c
index 0a1a522..c0606dd 100644
--- a/rect.c
+++ b/rect.c
@@ -386,7 +386,8 @@ static void display_grid(game_params *params, int *grid, int *numbers, int all)
 }
 #endif
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     int *grid, *numbers;
     struct rectlist *list;
@@ -898,6 +899,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return seed;
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     int area = params->w * params->h;
@@ -1703,6 +1709,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/sixteen.c b/sixteen.c
index 4611e3c..36c4281 100644
--- a/sixteen.c
+++ b/sixteen.c
@@ -172,7 +172,8 @@ static int perm_parity(int *perm, int n)
     return ret;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     int stop, n, i, x;
     int x1, x2, p1, p2;
@@ -278,6 +279,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return ret;
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 
 static char *validate_seed(game_params *params, char *seed)
 {
@@ -823,6 +829,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/solo.c b/solo.c
index c453b26..4b4adea 100644
--- a/solo.c
+++ b/solo.c
@@ -1351,7 +1351,8 @@ static int symmetries(game_params *params, int x, int y, int *output, int s)
     return i;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     int c = params->c, r = params->r, cr = c*r;
     int area = cr*cr;
@@ -1513,6 +1514,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return seed;
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     int area = params->r * params->r * params->c * params->c;
@@ -1959,6 +1965,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,
diff --git a/twiddle.c b/twiddle.c
index 162f68b..e296f48 100644
--- a/twiddle.c
+++ b/twiddle.c
@@ -291,7 +291,8 @@ static int grid_complete(int *grid, int wh, int orientable)
     return ok;
 }
 
-static char *new_game_seed(game_params *params, random_state *rs)
+static char *new_game_seed(game_params *params, random_state *rs,
+			   game_aux_info **aux)
 {
     int *grid;
     int w = params->w, h = params->h, n = params->n, wh = w*h;
@@ -358,6 +359,11 @@ static char *new_game_seed(game_params *params, random_state *rs)
     return ret;
 }
 
+void game_free_aux_info(game_aux_info *aux)
+{
+    assert(!"Shouldn't happen");
+}
+
 static char *validate_seed(game_params *params, char *seed)
 {
     char *p, *err;
@@ -985,6 +991,7 @@ const struct game thegame = {
     TRUE, game_configure, custom_params,
     validate_params,
     new_game_seed,
+    game_free_aux_info,
     validate_seed,
     new_game,
     dup_game,