diff --git a/src/main/java/puzzle/ExportFormat.java b/src/main/java/puzzle/ExportFormat.java
index 233adba..98669dd 100644
--- a/src/main/java/puzzle/ExportFormat.java
+++ b/src/main/java/puzzle/ExportFormat.java
@@ -49,12 +49,15 @@ public record ExportFormat() {
    
    record Bit(long[] bits) {
       
-      public Bit()                       { this(new long[(SIZE >> 6) + 1]); }
+      public Bit()                       { this(new long[2]); }
       static int wordIndex(int bitIndex) { return bitIndex >> 6; }
       public boolean get(int bitIndex)   { return (this.bits[wordIndex(bitIndex)] & 1L << bitIndex) != 0L; }
       public void set(int bitIndex)      { bits[wordIndex(bitIndex)] |= 1L << bitIndex; }
       public void clear(int bitIndex)    { this.bits[wordIndex(bitIndex)] &= ~(1L << bitIndex); }
-      public void clear()                { Arrays.fill(bits, 0L); }
+      public void clear() {
+         bits[0] = 0L;
+         bits[1] = 0L;
+      }
    }
    
    record Bit1029(long[] bits) {