diff --git a/R/utils.R b/R/utils.R
index 168b139..c3eeae8 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -92,7 +92,6 @@ in_dir = function(dir, expr) {
 
 #' Test if an object is identical to \code{FALSE}
 #'
-#' A simple abbreviation of \code{identical(x, FALSE)}.
 #' @param x An R object.
 #' @export
 #' @examples
@@ -100,7 +99,8 @@ in_dir = function(dir, expr) {
 #' isFALSE(TRUE)  # false
 #' isFALSE(FALSE)  # true
 #' isFALSE(c(FALSE, FALSE))  # false
-isFALSE = function(x) identical(x, FALSE)
+# TODO: replace by base::isFALSE() when min R for knitr will be 3.5.0
+isFALSE = function(x) is.logical(x) && length(x) == 1L && !is.na(x) && !x
 
 #' Parse R code and do not keep the source
 #'
diff --git a/man/isFALSE.Rd b/man/isFALSE.Rd
index a9074fe..248df95 100644
--- a/man/isFALSE.Rd
+++ b/man/isFALSE.Rd
@@ -10,7 +10,7 @@ isFALSE(x)
 \item{x}{An R object.}
 }
 \description{
-A simple abbreviation of \code{identical(x, FALSE)}.
+Test if an object is identical to \code{FALSE}
 }
 \examples{
 library(xfun)