diff --git a/R/nargin.R b/R/nargin.R
index e843e87..6ff20cc 100644
--- a/R/nargin.R
+++ b/R/nargin.R
@@ -3,9 +3,8 @@
 #' @return An integer
 #' @author Waldir Leoncio
 #' @note This function only makes sense inside another function
+#' @references https://stackoverflow.com/q/64422780/1169233
 nargin <- function() {
-	# FIXME: returning 0 because it is using its own envir instead of parent's
-	print(parent.env(environment()))
-	length(as.list(match.call(envir = parent.env(environment())))) - 1
-	# length(ls(envir=parent.env(environment()))) - 1
-}
\ No newline at end of file
+  if(sys.nframe() < 2) stop("must be called from inside a function")
+  length(as.list(sys.call(-1))) - 1
+}
diff --git a/man/nargin.Rd b/man/nargin.Rd
new file mode 100644
index 0000000..a7922a6
--- /dev/null
+++ b/man/nargin.Rd
@@ -0,0 +1,23 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/nargin.R
+\name{nargin}
+\alias{nargin}
+\title{Number of function input arguments}
+\usage{
+nargin()
+}
+\value{
+An integer
+}
+\description{
+Returns the number of arguments passed to the parent function
+}
+\note{
+This function only makes sense inside another function
+}
+\references{
+https://stackoverflow.com/q/64422780/1169233
+}
+\author{
+Waldir Leoncio
+}
diff --git a/tests/testthat/test-convertedBaseFunctions.R b/tests/testthat/test-convertedBaseFunctions.R
index bfc3fe8..11988f8 100644
--- a/tests/testthat/test-convertedBaseFunctions.R
+++ b/tests/testthat/test-convertedBaseFunctions.R
@@ -201,4 +201,20 @@ test_that("isspace works as expected", {
 	X <- '\t a b\tcde f'
 	expect_identical(isspace(chr), c(0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0))
 	expect_identical(isspace(X), c(1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0))
+})
+
+test_that("nargin works correctly", {
+	addme <- function(a, b) {
+		if (nargin() == 2) {
+			c <- a + b
+		} else if (nargin() == 1) {
+			c <- a + a
+		} else {
+			c <- 0
+		}
+		return(c)
+	}
+	expect_equal(addme(13, 42), 55)
+	expect_equal(addme(13), 26)
+	expect_equal(addme(), 0)
 })
\ No newline at end of file