diff --git a/render/loadsheet.go b/render/loadsheet.go
index 1db88a37..2d23313e 100644
--- a/render/loadsheet.go
+++ b/render/loadsheet.go
@@ -51,8 +51,15 @@ func MakeSheet(rgba *image.RGBA, cellSize intgeom.Point2) (*Sheet, error) {
 	bounds := rgba.Bounds()
 
 	sheetW := bounds.Max.X / w
+	wMod := bounds.Max.X % w
+	if wMod != 0 {
+		return nil, oakerr.InvalidInput{InputName: "cellSize.X"}
+	}
 	sheetH := bounds.Max.Y / h
-
+	hMod := bounds.Max.Y % h
+	if hMod != 0 {
+		return nil, oakerr.InvalidInput{InputName: "cellSize.Y"}
+	}
 	if sheetW < 1 || sheetH < 1 {
 		return nil, oakerr.InvalidInput{InputName: "cellSize"}
 	}
diff --git a/render/loadsheet_test.go b/render/loadsheet_test.go
index 1a079522..40079927 100644
--- a/render/loadsheet_test.go
+++ b/render/loadsheet_test.go
@@ -2,6 +2,7 @@ package render
 
 import (
 	"errors"
+	"image"
 	"os"
 	"path/filepath"
 	"testing"
@@ -72,3 +73,26 @@ func TestMakeSheet_BadDimensions(t *testing.T) {
 		t.Fatalf("expected invalid height, got %v", expected.InputName)
 	}
 }
+
+func TestMakeSheet_BadMod(t *testing.T) {
+	rgba := &image.RGBA{
+		Rect: image.Rect(0, 0, 10, 10),
+	}
+	_, err := MakeSheet(rgba, intgeom.Point2{4, 5})
+	expected := &oakerr.InvalidInput{}
+	if !errors.As(err, expected) {
+		t.Fatalf("expected invalid input error, got %v", err)
+	}
+	if expected.InputName != "cellSize.X" {
+		t.Fatalf("expected invalid width, got %v", expected.InputName)
+	}
+
+	_, err = MakeSheet(rgba, intgeom.Point2{5, 4})
+	expected = &oakerr.InvalidInput{}
+	if !errors.As(err, expected) {
+		t.Fatalf("expected invalid input error, got %v", err)
+	}
+	if expected.InputName != "cellSize.Y" {
+		t.Fatalf("expected invalid height, got %v", expected.InputName)
+	}
+}