diff --git a/main.c b/main.c
index d35e1de..9c1bf1a 100644
--- a/main.c
+++ b/main.c
@@ -19,6 +19,7 @@ typedef enum {
 	FOUND_MINE,
 	FOUND_SAFE,
 	FOUND_NOTHING,
+	FOUND_CONTRADICTION,
 } update_res_t;
 
 typedef struct {
@@ -66,6 +67,9 @@ static update_res_t update(state_t *state, int *x_out, int *y_out)
 		}
 	}
 
+	if (state->mines > NMINES || state->mines + state->unknown < NMINES)
+		return FOUND_CONTRADICTION;
+
 	for (int y = 0; y < HEIGHT; ++y) {
 		for (int x = 0; x < WIDTH; ++x) {
 			if (state->field[x][y] == UNKNOWN || state->field[x][y] == MINE
@@ -73,10 +77,16 @@ static update_res_t update(state_t *state, int *x_out, int *y_out)
 				continue;
 
 			const int mines = countadj(state->field, x, y, MINE);
+			if (mines > state->field[x][y])
+				return FOUND_CONTRADICTION;
+
 			const int unknowns = countadj(state->field, x, y, UNKNOWN);
 			if (unknowns == 0)
 				continue;
 
+			if (mines + unknowns < state->field[x][y])
+				return FOUND_CONTRADICTION;
+
 			if (mines + unknowns == state->field[x][y]) {
 				setadj(state->field, x, y, UNKNOWN, MINE);
 				return FOUND_MINE;
@@ -110,10 +120,11 @@ static status_t solve(int *turns_out)
 		    && (status = probe(x, y, state.field)) == DEAD)
 			break;
 
-		update_res_t update_res;
-		do
-			update_res = update(&state, &x, &y);
-		while (update_res == FOUND_MINE);
+		update_res_t res;
+		do {
+			res = update(&state, &x, &y);
+			assert(res != FOUND_CONTRADICTION);
+		} while (res == FOUND_MINE);
 
 		if (check(state.field) != OK) {
 			printf("Incorrect inference! State:\n");
@@ -122,7 +133,7 @@ static status_t solve(int *turns_out)
 			return INCORRECT;
 		}
 
-		if (update_res == FOUND_NOTHING) {
+		if (res == FOUND_NOTHING) {
 			x = rand() % WIDTH;
 			y = rand() % HEIGHT;
 		}