diff --git a/layouts/rowcol.go b/layouts/rowcol.go
index b239a5b..5bcaa90 100644
--- a/layouts/rowcol.go
+++ b/layouts/rowcol.go
@@ -41,12 +41,12 @@ func (row Row) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Poin
 
 func (column Column) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 	expands := func (index int) bool {
-		if index < len(boxes) { return false }
+		if index >= len(column) { return false }
 		return column[index]
 	}
 
 	// determine expanding box size
-	expandingSize := 0
+	expandingSize := 0.0
 	if !hints.OverflowY {
 		gaps       := len(boxes) - 1
 		freeSpace  := float64(hints.Bounds.Dy() - hints.Gap.Y * gaps)
@@ -83,7 +83,7 @@ func (column Column) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 			}
 		} else {
 			if expands(index) {
-				height = expandingSize
+				height = int(expandingSize)
 			}
 		}
 
@@ -111,12 +111,12 @@ func (column Column) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 
 func (row Row) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 	expands := func (index int) bool {
-		if index < len(boxes) { return false }
+		if index >= len(row) { return false }
 		return row[index]
 	}
 
 	// determine expanding box size
-	expandingSize := 0
+	expandingSize := 0.0
 	if !hints.OverflowY {
 		gaps       := len(boxes) - 1
 		freeSpace  := float64(hints.Bounds.Dx() - hints.Gap.X * gaps)
@@ -127,6 +127,7 @@ func (row Row) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 				freeSpace -= float64(box.MinimumSize().Y)
 			}
 		}
+		expandingSize = freeSpace / float64(nExpanding)
 	}
 
 	// determine height
@@ -153,7 +154,7 @@ func (row Row) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 			}
 		} else {
 			if expands(index) {
-				width = expandingSize
+				width = int(expandingSize)
 			}
 		}