diff --git a/common/bit_array.go b/common/bit_array.go
index eb314335b..034beb0f1 100644
--- a/common/bit_array.go
+++ b/common/bit_array.go
@@ -13,7 +13,11 @@ type BitArray struct {
 	Elems []uint64 `json:"elems"` // NOTE: persisted via reflect, must be exported
 }
 
+// There is no BitArray whose Size is 0.  Use nil instead.
 func NewBitArray(bits uint) *BitArray {
+	if bits == 0 {
+		return nil
+	}
 	return &BitArray{
 		Bits:  bits,
 		Elems: make([]uint64, (bits+63)/64),
@@ -168,10 +172,6 @@ func (bA *BitArray) IsFull() bool {
 	bA.mtx.Lock()
 	defer bA.mtx.Unlock()
 
-	if bA.Bits == 0 {
-		return false
-	}
-
 	// Check all elements except the last
 	for _, elem := range bA.Elems[:len(bA.Elems)-1] {
 		if (^elem) != 0 {