diff --git a/common/coords.go b/common/coords.go
index a3b2318..719073c 100644
--- a/common/coords.go
+++ b/common/coords.go
@@ -14,6 +14,8 @@ const (
 	numBitsPerComponent = 12
 	modulo              = 1 << numBitsPerComponent
 	maxPositive         = modulo / 2
+	minValue            = -1 << numBitsPerComponent
+	maxValue            = 1<<numBitsPerComponent - 1
 )
 
 type (
@@ -43,10 +45,6 @@ func (c Coord) String() string {
 	return fmt.Sprintf("(%d, %d, %d)", c.X, c.Y, c.Z)
 }
 
-func (c Coord) Equals(o Coord) bool {
-	return c.X == o.X && c.Y == o.Y && c.Z == o.Z
-}
-
 func minComponent(a, b int16) int16 {
 	if a < b {
 		return a
@@ -109,17 +107,20 @@ func DecodeFromBigEndian(key []byte) (int64, error) {
 
 func CoordToInterleaved(c Coord) (result int64) {
 	const end = 1 << (numBitsPerComponent + 1)
+	x := uint16(c.X - minValue)
+	y := uint16(c.Y - minValue)
+	z := uint16(c.Z - minValue)
 	setmask := int64(1)
-	for mask := int16(1); mask != end; mask <<= 1 {
-		if c.X&mask != 0 {
+	for mask := uint16(1); mask != end; mask <<= 1 {
+		if x&mask != 0 {
 			result |= setmask
 		}
 		setmask <<= 1
-		if c.Y&mask != 0 {
+		if y&mask != 0 {
 			result |= setmask
 		}
 		setmask <<= 1
-		if c.Z&mask != 0 {
+		if z&mask != 0 {
 			result |= setmask
 		}
 		setmask <<= 1
@@ -144,15 +145,9 @@ func InterleavedToCoord(pos int64) Coord {
 		}
 		pos >>= 1
 	}
-	if x >= 1<<numBitsPerComponent {
-		x -= end
-	}
-	if y >= 1<<numBitsPerComponent {
-		y -= end
-	}
-	if z >= 1<<numBitsPerComponent {
-		z -= end
-	}
+	x += minValue
+	y += minValue
+	z += minValue
 	return Coord{X: x, Y: y, Z: z}
 }
 
@@ -250,8 +245,7 @@ func NaiveBigMin(minz, maxz, zcode int64) int64 {
 }
 
 const (
-	bits = 12
-	msb  = uint8(3*bits - 1)
+	msb  = uint8(3*numBitsPerComponent - 1)
 	mask = int64(0x924924924)
 	full = int64(0xfffffffff)
 )
diff --git a/common/coords_test.go b/common/coords_test.go
index e34f640..36e866e 100644
--- a/common/coords_test.go
+++ b/common/coords_test.go
@@ -87,7 +87,7 @@ func checkJoinSplit(
 
 	k := join(c)
 	s := split(k)
-	if !s.Equals(c) {
+	if s != c {
 		t.Errorf("%s: Expected %s got %s %b\n", desc, c, s, k)
 	}
 }
@@ -153,6 +153,15 @@ func TestTransforms(t *testing.T) {
 	})
 }
 
+func TestCoordInterleaving(t *testing.T) {
+	allData(func(c Coord) {
+		d := InterleavedToCoord(CoordToInterleaved(c))
+		if c != d {
+			t.Errorf("Expected %v got %v\n", c, d)
+		}
+	})
+}
+
 func outsiders(zmin, zmax int64) chan int64 {
 
 	outs := make(chan int64)
@@ -200,6 +209,10 @@ func TestBigMin(t *testing.T) {
 		zmin := CoordToInterleaved(c1)
 		zmax := CoordToInterleaved(c2)
 
+		if zmin > zmax {
+			t.Errorf("zmin > zmax: %d > %d\n", zmin, zmax)
+		}
+
 		errors, success := 0, 0
 		for zcode := range outsiders(zmin, zmax) {
 			nbm := NaiveBigMin(zmin, zmax, zcode)
@@ -214,8 +227,9 @@ func TestBigMin(t *testing.T) {
 		}
 		if errors > 0 {
 			cub := Cuboid{P1: c1, P2: c2}
-			t.Errorf("BigMin: %s %d errors out of %d (%f)\n",
+			t.Errorf("BigMin: %s (%d %d) %d errors out of %d (%f)\n",
 				cub,
+				zmin, zmax,
 				errors, errors+success,
 				float64(errors)/float64(errors+success))
 		}