diff --git a/paws.common/R/time.R b/paws.common/R/time.R
index f9b42039e..b23c60c12 100644
--- a/paws.common/R/time.R
+++ b/paws.common/R/time.R
@@ -1,5 +1,5 @@
 # Returns a date value, given the number of seconds since Jan 1, 1970.
 unix_time <- function(sec, nsec = 0) {
-  time <- ISOdatetime(1970, 1, 1, 0, 0, 0, tz = "GMT") + as.numeric(sec)
-  return(time)
+  # origin: 1970-01-01 00:00:00
+  return(.POSIXct(as.numeric(sec), tz = "GMT"))
 }
diff --git a/paws.common/tests/testthat/test_dateutil.R b/paws.common/tests/testthat/test_dateutil.R
index 526893b6d..85cd2ed01 100644
--- a/paws.common/tests/testthat/test_dateutil.R
+++ b/paws.common/tests/testthat/test_dateutil.R
@@ -21,3 +21,39 @@ test_that("as_timestamp empty input", {
   exp <- as.POSIXct("", tz = "GMT", format = "foo")
   expect_equal(out, exp)
 })
+
+test_that("unix_time check default value", {
+  actual <- unix_time(0)
+  expect <- as.POSIXct("1970-01-01 00:00:00", tz = "GMT")
+  expect_equal(
+    actual,
+    expect
+  )
+})
+
+test_that("unix_time check numeric value", {
+  actual <- unix_time(1704067200)
+  expect <- as.POSIXct("2024-01-01 00:00:00", tz = "GMT")
+  expect_equal(
+    actual,
+    expect
+  )
+})
+
+test_that("unix_time check string value", {
+  actual <- unix_time("")
+  expect <- as.POSIXct(NA, tz = "GMT")
+  expect_equal(
+    actual,
+    expect
+  )
+})
+
+test_that("unix_time check null value", {
+  actual <- unix_time(NULL)
+  expect <- as.POSIXct(NULL, tz = "GMT")
+  expect_equal(
+    actual,
+    expect
+  )
+})