diff --git a/internal/affine/colorm.go b/internal/affine/colorm.go
index d47f80764..e33fb4109 100644
--- a/internal/affine/colorm.go
+++ b/internal/affine/colorm.go
@@ -41,7 +41,7 @@ var (
 // Before applying a matrix, a color is un-multiplied, and after applying the matrix,
 // the color is multiplied again.
 //
-// The initial value is identity.
+// The nil and initial value is identity.
 type ColorM struct {
 	// When elements is nil, this matrix is identity.
 	// elements are immutable and a new array must be created when updating.
diff --git a/internal/affine/geom.go b/internal/affine/geom.go
index 594a05e26..30fa6e82f 100644
--- a/internal/affine/geom.go
+++ b/internal/affine/geom.go
@@ -24,7 +24,9 @@ const GeoMDim = 3
 
 // A GeoM represents a matrix to transform geometry when rendering an image.
 //
-// The initial value is identity.
+// The nil value is identity.
+//
+// Note that the initial value GeoM{} is no longer identity. TODO: This is confusing. Fix this.
 type GeoM struct {
 	a  float64
 	b  float64