diff --git a/NEWS.md b/NEWS.md
index 21c97925..685aa781 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # scales (development version)
-
+* `fullseq()` and by extension `breaks_width()` can now deal with unsorted 
+  ranges (#435).
 * New `label_date_short(leading)` argument to replace leading zeroes (#442)
 * `breaks_pretty()` will return the input limit when it has no range (#446)
 * `transform_exp()` now has more sensible breaks, available in `breaks_exp()` 
diff --git a/R/full-seq.R b/R/full-seq.R
index 5d8c6bc1..1262737c 100644
--- a/R/full-seq.R
+++ b/R/full-seq.R
@@ -9,6 +9,7 @@ fullseq <- function(range, size, ...) UseMethod("fullseq")
 
 #' @export
 fullseq.numeric <- function(range, size, ..., pad = FALSE) {
+  range <- sort(range)
   if (zero_range(range)) {
     return(range + size * c(-1, 1) / 2)
   }
@@ -30,6 +31,7 @@ fullseq.numeric <- function(range, size, ..., pad = FALSE) {
 
 #' @export
 fullseq.Date <- function(range, size, ...) {
+  range <- sort(range)
   seq(floor_date(range[1], size), ceiling_date(range[2], size), by = size)
 }
 #' @export
@@ -37,6 +39,7 @@ fullseq.POSIXt <- function(range, size, ...) {
 
   # for subsecond interval support
   # seq() does not support partial secs in character strings
+  range <- sort(range)
   parsed <- parse_unit_spec(size)
   if (parsed$unit == "sec") {
     seq(floor_time(range[1], size), ceiling_time(range[2], size), by = parsed$mult)
@@ -53,6 +56,7 @@ fullseq.difftime <- function(range, size, ...) {
   }
 
   input_units <- units(range)
+  range <- sort(range)
 
   x <- seq(
     round_any(as.numeric(range[1], units = "secs"), size_seconds, floor),
diff --git a/tests/testthat/test-full-seq.R b/tests/testthat/test-full-seq.R
index e22329bd..9460c845 100644
--- a/tests/testthat/test-full-seq.R
+++ b/tests/testthat/test-full-seq.R
@@ -1,15 +1,17 @@
 test_that("works with numeric", {
   x <- c(0, 100)
-  expect_equal(fullseq(x, 50), c(0, 50, 100))
+  expected <- c(0, 50, 100)
+  expect_equal(fullseq(x, 50), expected)
+  expect_equal(fullseq(rev(x), 50), expected)
 })
 
 test_that("works with POSIXct", {
   x <- as.POSIXct(c("2000-01-01 08:29:58", "2000-01-01 08:30:10"), tz = "UTC")
 
-  expect_equal(
-    fullseq(x, "1 hour"),
-    as.POSIXct(c("2000-01-01 8:00:00 UTC", "2000-01-01 9:00:00 UTC"), tz = "UTC")
-  )
+  expected <- as.POSIXct(c("2000-01-01 8:00:00 UTC", "2000-01-01 9:00:00 UTC"), tz = "UTC")
+  expect_equal(fullseq(x, "1 hour"), expected)
+  expect_equal(fullseq(rev(x), "1 hour"), expected)
+
   expect_equal(
     fullseq(x, ".5 secs")[1:2],
     as.POSIXct(c("2000-01-01 08:29:58.0 UTC", "2000-01-01 08:29:58.5 UTC"), tz = "UTC")
@@ -17,8 +19,10 @@ test_that("works with POSIXct", {
 })
 
 test_that("works with Date", {
-  x <- as.Date("2012-01-01") + 1:30
-  expect_equal(fullseq(x, "1 month"), as.Date(c("2012-01-01", "2012-02-01")))
+  x <- as.Date("2012-01-01") + c(1, 30)
+  expected <- as.Date(c("2012-01-01", "2012-02-01", "2012-03-01"))
+  expect_equal(fullseq(x, "1 month"), expected)
+  expect_equal(fullseq(rev(x), "1 month"), expected)
 })
 
 test_that("works with hms/difftime", {
@@ -26,6 +30,7 @@ test_that("works with hms/difftime", {
   y <- as.difftime(c(0, 1800, 3600), units = "secs")
   expect_equal(fullseq(x, 1800), y)
   expect_equal(fullseq(x, "30 mins"), y)
+  expect_equal(fullseq(rev(x), "30 mins"), y)
 
   # Preserves units
   x <- as.difftime(c(0, 1), units = "hours")