diff --git a/mat64/matrix.go b/mat64/matrix.go
index ebbe4d51..71f102db 100644
--- a/mat64/matrix.go
+++ b/mat64/matrix.go
@@ -239,6 +239,12 @@ type Ler interface {
 	L(a Matrix)
 }
 
+// A BandWidther represents a banded matrix and can return the left and right half-bandwidths, k1 and
+// k2.
+type BandWidther interface {
+	BandWidth() (k1, k2 int)
+}
+
 // RawMatrix represents a cblas native representation of a matrix.
 type RawMatrix struct {
 	Order      blas.Order