diff --git a/solve.c b/solve.c
index b5cf04d..c1fc7f0 100644
--- a/solve.c
+++ b/solve.c
@@ -67,10 +67,8 @@ int solve(struct sudoku *sud)
 			 * cell in its row.
 			 */
 			valmask = 0;
-			for (j = 0; j < NGROUP; ++j) {
-				if (!DET(sud->cells[rowidx_lut[i][j]]))
-					valmask |= sud->cells[rowidx_lut[i][j]];
-			}
+			for (j = 0; j < NGROUP; ++j)
+				valmask |= sud->cells[rowidx_lut[i][j]];
 			if ((pvals = sud->cells[i] & ~valmask)) {
 				setpval(sud, i, pvals);
 				match = true;
@@ -82,10 +80,8 @@ int solve(struct sudoku *sud)
 			 * cell in its column.
 			 */
 			valmask = 0;
-			for (j = 0; j < NGROUP; ++j) {
-				if (!DET(sud->cells[colidx_lut[i][j]]))
-					valmask |= sud->cells[colidx_lut[i][j]];
-			}
+			for (j = 0; j < NGROUP; ++j)
+				valmask |= sud->cells[colidx_lut[i][j]];
 			if ((pvals = sud->cells[i] & ~valmask)) {
 				setpval(sud, i, pvals);
 				match = true;
@@ -97,10 +93,8 @@ int solve(struct sudoku *sud)
 			 * cell in its segment.
 			 */
 			valmask = 0;
-			for (j = 0; j < NGROUP; ++j) {
-				if (!DET(sud->cells[segidx_lut[i][j]]))
-					valmask |= sud->cells[segidx_lut[i][j]];
-			}
+			for (j = 0; j < NGROUP; ++j)
+				valmask |= sud->cells[segidx_lut[i][j]];
 			if ((pvals = sud->cells[i] & ~valmask)) {
 				setpval(sud, i, pvals);
 				match = true;
diff --git a/sud.c b/sud.c
index 51c8a21..70d41bf 100644
--- a/sud.c
+++ b/sud.c
@@ -70,6 +70,7 @@ enum update_res update(struct sudoku *sud, unsigned i, unsigned val)
 	}
 
 	/* Set the cell's value. */
+	sud->cells[i] = 0;
 	sud->cells[i] |= DETMASK;
 	sud->cells[i] |= val << VALSHIFT;