diff --git a/DESCRIPTION b/DESCRIPTION
index d2ba4aa..80de4b5 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -37,7 +37,7 @@ Suggests:
     lintr,
     Matrix
 VignetteBuilder: knitr
-RoxygenNote: 7.3.0
+RoxygenNote: 7.3.1
 Encoding: UTF-8
 Config/testthat/edition: 3
 SystemRequirements: C++17
diff --git a/NAMESPACE b/NAMESPACE
index 10b6161..663120e 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -15,7 +15,6 @@ importFrom(checkmate,assert_integer)
 importFrom(checkmate,assert_logical)
 importFrom(checkmate,assert_number)
 importFrom(checkmate,assert_numeric)
-importFrom(checkmate,assert_vector)
 importFrom(checkmate,check_matrix)
 importFrom(checkmate,check_numeric)
 importFrom(checkmate,test_atomic_vector)
diff --git a/R/diffusr-package.R b/R/diffusr-package.R
index eeb69b5..022d3d8 100644
--- a/R/diffusr-package.R
+++ b/R/diffusr-package.R
@@ -51,10 +51,5 @@
 #' @useDynLib diffusr
 #'
 #' @importFrom Rcpp sourceCpp
-#' @importFrom checkmate assert_vector
-#' @importFrom sparseMatrixStats colAnyNAs
 NULL
 
-.onAttach <- function(libname, pkgname) {
-  assert_vector(colAnyNAs(matrix(0)))
-}
diff --git a/R/is.dgCMatrix.R b/R/is.dgCMatrix.R
index d9e6a44..7ee5a0e 100644
--- a/R/is.dgCMatrix.R
+++ b/R/is.dgCMatrix.R
@@ -18,6 +18,8 @@ is.dgCMatrix <- function(mat) {
 #'
 #' @export
 #'
+#' @importFrom sparseMatrixStats colAnyNAs
+#'
 assert_dgCMatrix <- function(adj_matrix, non_negative = TRUE) {
   if (adj_matrix@Dim[1] != adj_matrix@Dim[2]) {
     stop(paste("Error: Assertion on 'adj_matrix' failed: Must have exactly",
@@ -29,5 +31,7 @@ assert_dgCMatrix <- function(adj_matrix, non_negative = TRUE) {
   } else if (non_negative && any(adj_matrix@x < 0)) {
     stop(paste("Error: Assertion on 'adj_matrix' failed: Element",
                seq_along(adj_matrix@x)[adj_matrix@x < 0][1], "is not >= 0."))
+  } else if (colAnyNAs(adj_matrix)) {
+    stop("Error: NAs in the matrix.")
   }
 }