diff --git a/exec/vector/src/main/java/org/apache/drill/exec/vector/accessor/writer/BitColumnWriter.java b/exec/vector/src/main/java/org/apache/drill/exec/vector/accessor/writer/BitColumnWriter.java
index 43cae140070..6d980b1888f 100644
--- a/exec/vector/src/main/java/org/apache/drill/exec/vector/accessor/writer/BitColumnWriter.java
+++ b/exec/vector/src/main/java/org/apache/drill/exec/vector/accessor/writer/BitColumnWriter.java
@@ -60,7 +60,7 @@ protected int prepareWrite() {
     // Please be thoughtful when changing the code.
 
     final int writeIndex = vectorIndex.vectorIndex();
-    prepareWrite(writeIndex);
+    prepareWrite(writeIndex - 1);
 
     // Track the last write location for zero-fill use next time around.
 
@@ -84,7 +84,7 @@ private void prepareWrite(int writeIndex) {
 
   @Override
   public void setValueCount(int valueCount) {
-    prepareWrite(valueCount);
+    prepareWrite(valueCount - 1);
     mutator.setValueCount(valueCount);
   }