diff --git a/net.c b/net.c
index de51f82..57d91d3 100644
--- a/net.c
+++ b/net.c
@@ -459,6 +459,11 @@ static int todo_get(struct todo *todo) {
     return ret;
 }
 
+/*
+ * Return values: -1 means puzzle was proved inconsistent, 0 means we
+ * failed to narrow down to a unique solution, +1 means we solved it
+ * fully.
+ */
 static int net_solver(int w, int h, unsigned char *tiles,
 		      unsigned char *barriers, int wrapping)
 {
@@ -733,7 +738,11 @@ static int net_solver(int w, int h, unsigned char *tiles,
 #endif
 	    }
 
-	    assert(j > 0);	       /* we can't lose _all_ possibilities! */
+	    if (j == 0) {
+                /* If we've ruled out all possible orientations for a
+                 * tile, then our puzzle has no solution at all. */
+                return -1;
+            }
 
 	    if (j < i) {
 		done_something = TRUE;
@@ -813,14 +822,14 @@ static int net_solver(int w, int h, unsigned char *tiles,
     /*
      * Mark all completely determined tiles as locked.
      */
-    j = TRUE;
+    j = +1;
     for (i = 0; i < w*h; i++) {
 	if (tilestate[i * 4 + 1] == 255) {
 	    assert(tilestate[i * 4 + 0] != 255);
 	    tiles[i] = tilestate[i * 4] | LOCKED;
 	} else {
 	    tiles[i] &= ~LOCKED;
-	    j = FALSE;
+	    j = 0;
 	}
     }
 
@@ -1334,7 +1343,7 @@ static char *new_game_desc(const game_params *params, random_state *rs,
 	/*
 	 * Run the solver to check unique solubility.
 	 */
-	while (!net_solver(w, h, tiles, NULL, params->wrapping)) {
+	while (net_solver(w, h, tiles, NULL, params->wrapping) != 1) {
 	    int n = 0;
 
 	    /*
@@ -1758,9 +1767,17 @@ static char *solve_game(const game_state *state, const game_state *currstate,
 	 * Run the internal solver on the provided grid. This might
 	 * not yield a complete solution.
 	 */
+        int solver_result;
+
 	memcpy(tiles, state->tiles, state->width * state->height);
-	net_solver(state->width, state->height, tiles,
-		   state->barriers, state->wrapping);
+	solver_result = net_solver(state->width, state->height, tiles,
+                                   state->barriers, state->wrapping);
+
+        if (solver_result < 0) {
+            *error = "No solution exists for this puzzle";
+            sfree(tiles);
+            return NULL;
+        }
     } else {
         for (i = 0; i < state->width * state->height; i++) {
             int c = aux[i];