diff --git a/NAMESPACE b/NAMESPACE
index 5b79434ba..4882faaa7 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -19,6 +19,7 @@ export(create_font)
 export(create_hyperlink)
 export(create_numfmt)
 export(create_sparklines)
+export(current_sheet)
 export(dataframe_to_dims)
 export(delete_data)
 export(dims_to_dataframe)
@@ -28,6 +29,8 @@ export(get_date_origin)
 export(get_named_regions)
 export(guess_col_type)
 export(int2col)
+export(na_strings)
+export(next_sheet)
 export(read_sheet_names)
 export(read_xlsx)
 export(read_xml)
diff --git a/NEWS.md b/NEWS.md
index 69814ce2b..b7ddf2dba 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -13,6 +13,10 @@
 
 * Improve date detection in `wb_to_df()`. This improves date and posix detection with custom date formats. [547](https://github.com/JanMarvin/openxlsx2/pull/547)
 
+* `na_strings()` is now used as the explicit default value for `na.strings` parameters in exported workbook functions ([#473](https://github.com/ycphs/openxlsx/issues/473))
+
+* waiver functions (i.e., `next_worksheet()`, `current_worksheet()`, and `na_strings()`) are now exports ([#474](https://github.com/ycphs/openxlsx/issues/474))
+
 ## Fixes
 
 * Fixed a bug when loading input with multiple sheets where not every sheet contains a drawing/comment. Previously we assumed that every sheet had a comment and ordered them incorrectly. This caused confusion in spreadsheet software. [536](https://github.com/JanMarvin/openxlsx2/pull/536)
@@ -64,7 +68,6 @@
 
 * Only documentation: `openxlsx2` defaults to American English 'color' from now on. Though, we fully support the previous 'colour'. Users will not have to adjust their code. Our documentation only lists `color`, but you can pass `colour` just the same way you used to. [501](https://github.com/JanMarvin/openxlsx2/pull/501) [502](https://github.com/JanMarvin/openxlsx2/pull/502)
 
-
 ***************************************************************************
 
 
diff --git a/R/class-workbook-utils.R b/R/class-workbook-utils.R
index 0bfd459d2..9396ad32d 100644
--- a/R/class-workbook-utils.R
+++ b/R/class-workbook-utils.R
@@ -150,14 +150,38 @@ validate_cf_params <- function(params) {
 
 # waivers -----------------------------------------------------------------
 
+#' `openxlsx2` waivers
+#'
+#' Waiver functions for `openxlsx2` functions
+#'
+#' @name waivers
+#' @returns An object of class `openxlsx2_waiver`
+NULL
+
+#' @rdname waivers
+#' @export
 current_sheet <- function() {
   structure("current_sheet", class = "openxlsx2_waiver")
 }
 
+#' @rdname waivers
+#' @export
 next_sheet <- function() {
   structure("next_sheet", class = "openxlsx2_waiver")
 }
 
+#' @rdname waivers
+#' @export
+na_strings <- function() {
+  structure("na_strings", class = "openxlsx2_waiver")
+}
+
+# helpers -----------------------------------------------------------------
+
 is_waiver <- function(x) {
   inherits(x, "openxlsx2_waiver")
 }
+
+is_na_strings <- function(x) {
+  is_waiver(x) && isTRUE(x == "na_strings")
+}
diff --git a/R/class-workbook-wrappers.R b/R/class-workbook-wrappers.R
index bd3822245..45b120908 100644
--- a/R/class-workbook-wrappers.R
+++ b/R/class-workbook-wrappers.R
@@ -90,7 +90,8 @@ wb_save <- function(wb, path = NULL, overwrite = TRUE) {
 #' @param sep Only applies to list columns. The separator used to collapse list columns to a character vector e.g. sapply(x$list_column, paste, collapse = sep).
 #' @param applyCellStyle Should we write cell styles to the workbook
 #' @param removeCellStyle keep the cell style?
-#' @param na.strings na.strings
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.
 #' @param inline_strings write characters as inline strings
 #' @export
 #' @details Formulae written using write_formula to a Workbook object will not get picked up by read_xlsx().
@@ -115,13 +116,10 @@ wb_add_data <- function(
     sep             = ", ",
     applyCellStyle  = TRUE,
     removeCellStyle = FALSE,
-    na.strings,
+    na.strings      = na_strings(),
     inline_strings  = TRUE
 ) {
   assert_workbook(wb)
-
-  if (missing(na.strings)) na.strings <- substitute()
-
   wb$clone(deep = TRUE)$add_data(
     sheet           = sheet,
     x               = x,
@@ -175,7 +173,8 @@ wb_add_data <- function(
 #' @param bandedCols logical. If TRUE, the columns are color banded
 #' @param applyCellStyle Should we write cell styles to the workbook
 #' @param removeCellStyle keep the cell style?
-#' @param na.strings optional
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.
 #' @param inline_strings write characters as inline strings
 #'
 #' @details columns of x with class Date/POSIXt, currency, accounting,
@@ -205,12 +204,10 @@ wb_add_data_table <- function(
     bandedCols  = FALSE,
     applyCellStyle  = TRUE,
     removeCellStyle = FALSE,
-    na.strings,
+    na.strings     = na_strings(),
     inline_strings = TRUE
 ) {
   assert_workbook(wb)
-  if (missing(na.strings)) na.strings <- substitute()
-
   wb$clone()$add_data_table(
     sheet       = sheet,
     x           = x,
diff --git a/R/class-workbook.R b/R/class-workbook.R
index cadd05352..887c6d986 100644
--- a/R/class-workbook.R
+++ b/R/class-workbook.R
@@ -1031,7 +1031,8 @@ wbWorkbook <- R6::R6Class(
     #' @param sep sep
     #' @param applyCellStyle applyCellStyle
     #' @param removeCellStyle if writing into existing cells, should the cell style be removed?
-    #' @param na.strings na.strings
+    #' @param na.strings Value used for replacing `NA` values from `x`. Default
+    #'   `na_strings()` uses the special `#N/A` value within the workbook.
     #' @param inline_strings write characters as inline strings
     #' @param return The `wbWorkbook` object
     add_data = function(
@@ -1049,12 +1050,10 @@ wbWorkbook <- R6::R6Class(
         sep             = ", ",
         applyCellStyle  = TRUE,
         removeCellStyle = FALSE,
-        na.strings,
+        na.strings      = na_strings(),
         inline_strings  = TRUE
       ) {
 
-      if (missing(na.strings)) na.strings <- substitute()
-
       write_data(
         wb              = self,
         sheet           = sheet,
@@ -1096,7 +1095,8 @@ wbWorkbook <- R6::R6Class(
     #' @param bandedCols bandedCols
     #' @param applyCellStyle applyCellStyle
     #' @param removeCellStyle if writing into existing cells, should the cell style be removed?
-    #' @param na.strings na.strings
+    #' @param na.strings Value used for replacing `NA` values from `x`. Default
+    #'   `na_strings()` uses the special `#N/A` value within the workbook.
     #' @param inline_strings write characters as inline strings
     #' @returns The `wbWorkbook` object
     add_data_table = function(
@@ -1118,12 +1118,10 @@ wbWorkbook <- R6::R6Class(
         bandedCols      = FALSE,
         applyCellStyle  = TRUE,
         removeCellStyle = FALSE,
-        na.strings,
+        na.strings      = na_strings(),
         inline_strings  = TRUE
     ) {
 
-      if (missing(na.strings)) na.strings <- substitute()
-
       write_datatable(
         wb              = self,
         sheet           = sheet,
diff --git a/R/write.R b/R/write.R
index 42b24530a..b8e69da56 100644
--- a/R/write.R
+++ b/R/write.R
@@ -9,8 +9,8 @@
 #' @param cells_needed the cells needed
 #' @param colNames has colNames (only in update_cell)
 #' @param removeCellStyle remove the cell style (only in update_cell)
-#' @param na.strings optional na.string (only in update_cell)
-#' @keywords internal
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.#' @keywords internal
 #' @noRd
 inner_update <- function(
     wb,
@@ -20,7 +20,7 @@ inner_update <- function(
     cells_needed,
     colNames = FALSE,
     removeCellStyle = FALSE,
-    na.strings
+    na.strings = na_strings()
 ) {
 
   # 1) pull sheet to modify from workbook; 2) modify it; 3) push it back
@@ -82,7 +82,7 @@ inner_update <- function(
     wb$worksheets[[sheet_id]]$dimension <- paste0("<dimension ref=\"", min_cell, ":", max_cell, "\"/>")
   }
 
-  if (missing(na.strings)) {
+  if (is_na_strings(na.strings)) {
     na.strings <- NULL
   }
 
@@ -189,7 +189,8 @@ nmfmt_df <- function(x) {
 #' @param startCol col to place it
 #' @param applyCellStyle apply styles when writing on the sheet
 #' @param removeCellStyle keep the cell style?
-#' @param na.strings optional na.strings argument. if missing #N/A is used. If NULL no cell value is written, if character or numeric this is written (even if NA is part of numeric data)
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.
 #' @param data_table logical. if `TRUE` and `rowNames = TRUE`, do not write the cell containing  `"_rowNames_"`
 #' @param inline_strings write characters as inline strings
 #' @details
@@ -224,13 +225,11 @@ write_data2 <- function(
     startCol = 1,
     applyCellStyle = TRUE,
     removeCellStyle = FALSE,
-    na.strings,
+    na.strings = na_strings(),
     data_table = FALSE,
     inline_strings = TRUE
 ) {
 
-  if (missing(na.strings)) na.strings <- substitute()
-
   is_data_frame <- FALSE
   #### prepare the correct data formats for openxml
   dc <- openxlsx2_type(data)
@@ -358,7 +357,8 @@ write_data2 <- function(
 
   na_missing <- FALSE
   na_null    <- FALSE
-  if (missing(na.strings)) {
+
+  if (is_na_strings(na.strings)) {
     na.strings <- ""
     na_missing <- TRUE
   } else if (is.null(na.strings)) {
@@ -661,7 +661,8 @@ write_data2 <- function(
 #' @param name If not NULL, a named region is defined.
 #' @param applyCellStyle apply styles when writing on the sheet
 #' @param removeCellStyle if writing into existing cells, should the cell style be removed?
-#' @param na.strings optional na.strings argument. if missing #N/A is used. If NULL no cell value is written, if character or numeric this is written (even if NA is part of numeric data)
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.
 #' @param inline_strings optional write strings as inline strings
 #' @noRd
 write_data_table <- function(
@@ -687,7 +688,7 @@ write_data_table <- function(
     applyCellStyle = TRUE,
     removeCellStyle = FALSE,
     data_table = FALSE,
-    na.strings,
+    na.strings = na_strings(),
     inline_strings = TRUE
 ) {
 
@@ -715,8 +716,6 @@ write_data_table <- function(
     startRow <- min(dims[[2]])
   }
 
-  if (missing(na.strings)) na.strings <- substitute()
-
   ## common part ---------------------------------------------------------------
   if ((!is.character(sep)) || (length(sep) != 1))
     stop("sep must be a character vector of length 1")
@@ -946,7 +945,8 @@ write_data_table <- function(
 #' @param name If not NULL, a named region is defined.
 #' @param applyCellStyle apply styles when writing on the sheet
 #' @param removeCellStyle if writing into existing cells, should the cell style be removed?
-#' @param na.strings optional na.strings argument. if missing #N/A is used. If NULL no cell value is written, if character or numeric this is written (even if NA is part of numeric data)
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.
 #' @param inline_strings write characters as inline strings
 #' @seealso [write_datatable()]
 #' @export write_data
@@ -1024,12 +1024,10 @@ write_data <- function(
     name = NULL,
     applyCellStyle = TRUE,
     removeCellStyle = FALSE,
-    na.strings,
+    na.strings = na_strings(),
     inline_strings = TRUE
 ) {
 
-  if (missing(na.strings)) na.strings <- substitute()
-
   write_data_table(
     wb = wb,
     sheet = sheet,
@@ -1219,7 +1217,8 @@ write_formula <- function(
 #' @param bandedCols logical. If TRUE, the columns are color banded
 #' @param applyCellStyle apply styles when writing on the sheet
 #' @param removeCellStyle if writing into existing cells, should the cell style be removed?
-#' @param na.strings optional na.strings argument. if missing #N/A is used. If NULL no cell value is written, if character or numeric this is written (even if NA is part of numeric data)
+#' @param na.strings Value used for replacing `NA` values from `x`. Default
+#'   `na_strings()` uses the special `#N/A` value within the workbook.
 #' @param inline_strings write characters as inline strings
 #' @details columns of x with class Date/POSIXt, currency, accounting,
 #' hyperlink, percentage are automatically styled as dates, currency, accounting,
@@ -1333,12 +1332,10 @@ write_datatable <- function(
     bandedCols = FALSE,
     applyCellStyle = TRUE,
     removeCellStyle = FALSE,
-    na.strings,
+    na.strings = na_strings(),
     inline_strings = TRUE
 ) {
 
-  if (missing(na.strings)) na.strings <- substitute()
-
   write_data_table(
     wb = wb,
     sheet = sheet,
diff --git a/R/write_xlsx.R b/R/write_xlsx.R
index 74cffd4d3..3cfbbf980 100644
--- a/R/write_xlsx.R
+++ b/R/write_xlsx.R
@@ -286,10 +286,7 @@ write_xlsx <- function(x, file, asTable = FALSE, ...) {
     tableStyle <- params$tableStyle
   }
 
-  na_strings <- substitute()
-  if ("na.strings" %in% names(params)) {
-    na_strings <- params$na.strings
-  }
+  na.strings <- params$na.strings %||% na_strings()
 
 
   ## create new Workbook object
@@ -380,7 +377,7 @@ write_xlsx <- function(x, file, asTable = FALSE, ...) {
         tableStyle = tableStyle[[i]],
         tableName = NULL,
         withFilter = withFilter[[i]],
-        na.strings = na_strings
+        na.strings = na.strings
       )
     } else {
       write_data(
@@ -392,7 +389,7 @@ write_xlsx <- function(x, file, asTable = FALSE, ...) {
         xy = xy,
         colNames = colNames[[i]],
         rowNames = rowNames[[i]],
-        na.strings = na_strings
+        na.strings = na.strings
       )
     }
 
diff --git a/man/waivers.Rd b/man/waivers.Rd
new file mode 100644
index 000000000..e1cb86585
--- /dev/null
+++ b/man/waivers.Rd
@@ -0,0 +1,21 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/class-workbook-utils.R
+\name{waivers}
+\alias{waivers}
+\alias{current_sheet}
+\alias{next_sheet}
+\alias{na_strings}
+\title{\code{openxlsx2} waivers}
+\usage{
+current_sheet()
+
+next_sheet()
+
+na_strings()
+}
+\value{
+An object of class \code{openxlsx2_waiver}
+}
+\description{
+Waiver functions for \code{openxlsx2} functions
+}
diff --git a/man/wbWorkbook.Rd b/man/wbWorkbook.Rd
index 45e08a0dc..8736ad103 100644
--- a/man/wbWorkbook.Rd
+++ b/man/wbWorkbook.Rd
@@ -575,7 +575,7 @@ add data
   sep = ", ",
   applyCellStyle = TRUE,
   removeCellStyle = FALSE,
-  na.strings,
+  na.strings = na_strings(),
   inline_strings = TRUE
 )}\if{html}{\out{</div>}}
 }
@@ -611,7 +611,8 @@ add data
 
 \item{\code{removeCellStyle}}{if writing into existing cells, should the cell style be removed?}
 
-\item{\code{na.strings}}{na.strings}
+\item{\code{na.strings}}{Value used for replacing \code{NA} values from \code{x}. Default
+\code{na_strings()} uses the special \verb{#N/A} value within the workbook.}
 
 \item{\code{inline_strings}}{write characters as inline strings}
 
@@ -645,7 +646,7 @@ add a data table
   bandedCols = FALSE,
   applyCellStyle = TRUE,
   removeCellStyle = FALSE,
-  na.strings,
+  na.strings = na_strings(),
   inline_strings = TRUE
 )}\if{html}{\out{</div>}}
 }
@@ -689,7 +690,8 @@ add a data table
 
 \item{\code{removeCellStyle}}{if writing into existing cells, should the cell style be removed?}
 
-\item{\code{na.strings}}{na.strings}
+\item{\code{na.strings}}{Value used for replacing \code{NA} values from \code{x}. Default
+\code{na_strings()} uses the special \verb{#N/A} value within the workbook.}
 
 \item{\code{inline_strings}}{write characters as inline strings}
 }
diff --git a/man/wb_add_data_table.Rd b/man/wb_add_data_table.Rd
index f7cb8e966..3921dfa24 100644
--- a/man/wb_add_data_table.Rd
+++ b/man/wb_add_data_table.Rd
@@ -24,7 +24,7 @@ wb_add_data_table(
   bandedCols = FALSE,
   applyCellStyle = TRUE,
   removeCellStyle = FALSE,
-  na.strings,
+  na.strings = na_strings(),
   inline_strings = TRUE
 )
 }
@@ -76,7 +76,8 @@ sep).
 
 \item{removeCellStyle}{keep the cell style?}
 
-\item{na.strings}{optional}
+\item{na.strings}{Value used for replacing \code{NA} values from \code{x}. Default
+\code{na_strings()} uses the special \verb{#N/A} value within the workbook.}
 
 \item{inline_strings}{write characters as inline strings}
 }
diff --git a/man/write_data.Rd b/man/write_data.Rd
index 3df956229..67203283c 100644
--- a/man/write_data.Rd
+++ b/man/write_data.Rd
@@ -21,7 +21,7 @@ wb_add_data(
   sep = ", ",
   applyCellStyle = TRUE,
   removeCellStyle = FALSE,
-  na.strings,
+  na.strings = na_strings(),
   inline_strings = TRUE
 )
 
@@ -41,7 +41,7 @@ write_data(
   name = NULL,
   applyCellStyle = TRUE,
   removeCellStyle = FALSE,
-  na.strings,
+  na.strings = na_strings(),
   inline_strings = TRUE
 )
 }
@@ -78,7 +78,8 @@ write_data(
 
 \item{removeCellStyle}{if writing into existing cells, should the cell style be removed?}
 
-\item{na.strings}{optional na.strings argument. if missing #N/A is used. If NULL no cell value is written, if character or numeric this is written (even if NA is part of numeric data)}
+\item{na.strings}{Value used for replacing \code{NA} values from \code{x}. Default
+\code{na_strings()} uses the special \verb{#N/A} value within the workbook.}
 
 \item{inline_strings}{write characters as inline strings}
 }
diff --git a/man/write_datatable.Rd b/man/write_datatable.Rd
index 531dc36c8..6b1abac20 100644
--- a/man/write_datatable.Rd
+++ b/man/write_datatable.Rd
@@ -24,7 +24,7 @@ write_datatable(
   bandedCols = FALSE,
   applyCellStyle = TRUE,
   removeCellStyle = FALSE,
-  na.strings,
+  na.strings = na_strings(),
   inline_strings = TRUE
 )
 }
@@ -73,7 +73,8 @@ A vector of the form c(startCol, startRow)}
 
 \item{removeCellStyle}{if writing into existing cells, should the cell style be removed?}
 
-\item{na.strings}{optional na.strings argument. if missing #N/A is used. If NULL no cell value is written, if character or numeric this is written (even if NA is part of numeric data)}
+\item{na.strings}{Value used for replacing \code{NA} values from \code{x}. Default
+\code{na_strings()} uses the special \verb{#N/A} value within the workbook.}
 
 \item{inline_strings}{write characters as inline strings}
 }