diff --git a/src/main/java/puzzle/Export.java b/src/main/java/puzzle/Export.java
index 8763df1..7125dc5 100644
--- a/src/main/java/puzzle/Export.java
+++ b/src/main/java/puzzle/Export.java
@@ -108,7 +108,10 @@ public record Export() {
          }
       }
       //public boolean isLetterSet(int idx)                { return isLetter(g[idx]); }
-      char NOT_CLUE_NOT_LETTER_TO(byte b, char fallback) { return b == SwedishGenerator.DASH ? fallback : (char) (64 | b); }
+      char NOT_CLUE_NOT_LETTER_TO(byte b, char fallback) {
+         if (b == SwedishGenerator.DASH) throw new RuntimeException();
+         return (char) (64 | b);
+      }
       String gridToString(Clues clues) {
          var sb = new StringBuilder();
          for (var r = 0; r < R; r++) {
@@ -117,8 +120,10 @@ public record Export() {
                var offset = Grid.offset(r, c);
                if (clues.isClue(offset))
                   sb.append((char) (48 | clues.digitAt(offset)));
-               else
+               else if (grid.lisLetterAtLo(offset))
                   sb.append((char) (64 | grid.letter32At(offset)));
+               else
+                  sb.append(' ');
             }
          }
          return sb.toString();
@@ -140,8 +145,10 @@ public record Export() {
                var offset = Grid.offset(r, c);
                if (clues.isClue(offset)) {
                   sb.append(clueChar.replace(new Cell(grid, clues, offset, clues.digitAt(offset))));
-               } else {
+               } else if (grid.lisLetterAt(offset)) {
                   sb.append(NOT_CLUE_NOT_LETTER_TO(grid.letter32At(offset), emptyFallback));
+               } else {
+                  sb.append(emptyFallback);
                }
             }
             out[r] = sb.toString();
@@ -229,7 +236,8 @@ public record Export() {
          var letterAt = new HashMap<Integer, Character>();
          for (var p : placed) {
             for (var c : p.cells) {
-               if (inBounds(c) && mask.notClue(c)) {
+               if (!inBounds(c)) throw new RuntimeException();
+               if (mask.notClue(c) && g.lisLetterAt(c)) {
                   letterAt.put(c, (char) (64 | g.letter32At(c)));
                }
             }
diff --git a/src/main/java/puzzle/SwedishGenerator.java b/src/main/java/puzzle/SwedishGenerator.java
index 5068b3a..ab1303a 100644
--- a/src/main/java/puzzle/SwedishGenerator.java
+++ b/src/main/java/puzzle/SwedishGenerator.java
@@ -285,6 +285,14 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
       static int offset(int r, int c) { return r | (c << 3); }
       /// the pos will never target a clue
       public byte letter32At(int pos) { return g[pos]; }
+      public boolean lisLetterAt(int pos) {
+         if ((pos & 64) == 0)
+            return lisLetterAtLo(pos);
+         return lisLetterAtHi(pos);
+      }
+      
+      public boolean lisLetterAtLo(int pos) { return (lo & (1L << pos)) != 0; }
+      public boolean lisLetterAtHi(int pos) { return (hi & (1L << (pos & 63))) != 0; }
       void setLetterLo(int idx, byte ch) {
          lo |= (1L << idx);
          
@@ -313,8 +321,11 @@ public record SwedishGenerator(Rng rng, int[] stack, Clues cache) {
          hi &= ~(1L << (idx & 63));
       }
       void undoPlace(long maskLo, long maskHi) {
-         for (long b = maskLo; b != 0; b &= b - 1) clearletterLo(Long.numberOfTrailingZeros(b));
-         for (long b = maskHi; b != 0; b &= b - 1) clearletterHi(64 | Long.numberOfTrailingZeros(b));
+         lo &= ~maskLo;
+         hi &= ~maskHi;
+         
+         /*for (long b = maskLo; b != 0; b &= b - 1) clearletterLo(Long.numberOfTrailingZeros(b));
+         for (long b = maskHi; b != 0; b &= b - 1) clearletterHi(64 | Long.numberOfTrailingZeros(b));*/
       }
    }
    
diff --git a/src/test/java/puzzle/MainTest.java b/src/test/java/puzzle/MainTest.java
index eb6334f..4a7f745 100644
--- a/src/test/java/puzzle/MainTest.java
+++ b/src/test/java/puzzle/MainTest.java
@@ -14,7 +14,6 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static puzzle.SwedishGenerator.*;
-import static puzzle.SwedishGenerator.DASH;
 
 public class MainTest {
    
@@ -107,13 +106,13 @@ public class MainTest {
       Assertions.assertEquals(LETTER_A, grid.letter32At(OFF_0_0));
       Assertions.assertEquals(CLUE_UP, clues.digitAt(OFF_1_2));
       Assertions.assertEquals(LETTER_Z, grid.letter32At(OFF_2_3));
-      Assertions.assertEquals(DASH, grid.letter32At(OFF_1_1));
+      Assertions.assertFalse(grid.lisLetterAtLo(OFF_1_1));
       
       // Verify letter mask
       Assertions.assertTrue((grid.lo & (1L << OFF_0_0)) != 0);
       Assertions.assertTrue((grid.lo & (1L << OFF_2_3)) != 0);
       Assertions.assertTrue((grid.lo & (1L << OFF_1_2)) != 0); // Clue also in lo
-      Assertions.assertTrue((grid.lo & (1L << OFF_1_1)) == 0); // Empty letter cell
+      assertEquals(0, (grid.lo & (1L << OFF_1_1))); // Empty letter cell
       
       // Test isLetterAt
       Assertions.assertTrue(clues.notClue(OFF_0_0));
diff --git a/src/test/java/puzzle/SwedishGeneratorTest.java b/src/test/java/puzzle/SwedishGeneratorTest.java
index a27b455..5efdf53 100644
--- a/src/test/java/puzzle/SwedishGeneratorTest.java
+++ b/src/test/java/puzzle/SwedishGeneratorTest.java
@@ -100,7 +100,7 @@ public class SwedishGeneratorTest {
    
    @Test
    void testPatternForSlotAllDashes() {
-      var grid = createEmpty();
+      var grid    = createEmpty();
       var slot    = Slot.from(1 << Slot.BIT_FOR_DIR | (CLUE_RIGHT), 7L, 0L);
       var pattern = patternForSlot(grid, slot);
       
@@ -360,8 +360,8 @@ public class SwedishGeneratorTest {
       grid.setLetter(OFF_0_2, LETTER_X); // Conflict at the end
       assertFalse(placeWord(grid, s, w1, undoBuffer, 3));
       // Verify grid is still empty (except for 'X')
-      assertEquals(DASH, grid.letter32At(OFF_0_0));
-      assertEquals(DASH, grid.letter32At(OFF_0_1));
+      assertFalse(grid.lisLetterAtLo(OFF_0_0));
+      assertFalse(grid.lisLetterAtLo(OFF_0_1));
       assertEquals(LETTER_X, grid.letter32At(OFF_0_2));
    }
    
@@ -382,8 +382,8 @@ public class SwedishGeneratorTest {
       assertEquals(lo, undoBuffer[0]);
       
       grid.undoPlace(undoBuffer[0], undoBuffer[1]);
-      assertEquals(DASH, grid.letter32At(OFF_0_1));
-      assertEquals(DASH, grid.letter32At(OFF_0_2));
+      assertFalse(grid.lisLetterAtLo(OFF_0_1));
+      assertFalse(grid.lisLetterAtLo(OFF_0_2));
    }
    
    @Test