diff --git a/R/argument_checking.R b/R/argument_checking.R
index 7ab1390..551d346 100644
--- a/R/argument_checking.R
+++ b/R/argument_checking.R
@@ -1,7 +1,7 @@
 # Return true if x is a compressed, sparse, column-oriented numeric
 # matrix.
 is.sparse.matrix <- function (x)
-  (inherits(x,"dgCMatrix") || inherits(x,"dgTMatrix")) && is.numeric(x@x)
+  inherits(x,"dsparseMatrix") && is.numeric(x@x)
 
 # Verify that x is matrix with finite, numeric entries.
 verify.matrix <- function (x, arg.name = deparse(substitute(x))) {