diff --git a/R/duplicated.R b/R/duplicated.R
index c5a89f115..b8359f31e 100644
--- a/R/duplicated.R
+++ b/R/duplicated.R
@@ -90,6 +90,7 @@ anyDuplicated.data.table <- function(x, incomparables=FALSE, fromLast=FALSE, by=
 # simple straightforward helper function to get the number 
 # of groups in a vector or data.table. Here by data.table, 
 # we really mean `.SD` - used in a grouping operation
+# TODO: optimise uniqueN further with GForce.
 uniqueN <- function(x, by = if (is.data.table(x)) key(x) else NULL, na.rm=FALSE) { # na.rm, #1455
     if (is.null(x)) return(0L)
     if (!is.atomic(x) && !is.data.frame(x))
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index 00190cae4..a8f0f53b2 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -7801,7 +7801,7 @@ test(1627, charToRaw(names(fread("issue_1087_utf8_bom.csv"))[1L]), as.raw(97L))
 
 # uniqueN gains na.rm argument, #1455
 set.seed(1L)
-dt = data.table(x=sample(3,25,TRUE), y=sample(c(NA,"a", "b"), 25,TRUE), z=sample(2,25,TRUE))
+dt = data.table(x=sample(c(1:3,NA),25,TRUE), y=sample(c(NA,"a", "b"), 25,TRUE), z=sample(2,25,TRUE))
 test(1628.1, uniqueN(dt, by=1:2, na.rm=TRUE), nrow(na.omit(dt[, .N, by=.(x,y)])))
 test(1628.2, uniqueN(dt, na.rm=TRUE), nrow(na.omit(dt[, .N, by=.(x,y,z)])))
 test(1628.3, dt[, uniqueN(y, na.rm=TRUE), by=z], dt[, length(unique(na.omit(y))), by=z])