diff --git a/NEWS.md b/NEWS.md
index 4f4a2f417a..e75ed6901f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -292,7 +292,7 @@
     # 2:     2    10
     ```
 
-40.  New functions `yearmon()` and `yearqtr` give a combined representation of `year()` and `month()`/`quarter()`. These and also `yday`, `wday`, `mday`, `week`, `month` and `year` are now optimized for memory and compute efficiency by removing the `POSIXlt` dependency, [#649](https://github.com/Rdatatable/data.table/issues/649). Thanks to Matt Dowle for the request, and Benjamin Schwendinger for the PR.
+40.  New functions `yearmon()` and `yearqtr` give a combined representation of `year()` and `month()`/`quarter()`. These and also `yday`, `wday`, `mday`, `week`, `month` and `year` are now optimized for memory and compute efficiency by removing the `POSIXlt` dependency, [#649](https://github.com/Rdatatable/data.table/issues/649). Thanks to Matt Dowle for the request, and Benjamin Schwendinger for the PR. Thanks to @berg-michael for testing dev and filing a bug report for special case of missing values which was fixed before release.
 
 41. New function `%notin%` provides a convenient alternative to `!(x %in% y)`, [#4152](https://github.com/Rdatatable/data.table/issues/4152). Thanks to Jan Gorecki for suggesting and Michael Czekanski for the PR. `%notin%` uses half the memory because it computes the result directly as opposed to `!` which allocates a new vector to hold the negated result. If `x` is long enough to occupy more than half the remaining free memory, this can make the difference between the operation working, or failing with an out-of-memory error.
 
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index e05f522814..1e1e74ce69 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -18786,16 +18786,16 @@ test(2235.1, copy(DT)[, c("z", "x") := {x = NULL; list(2, NULL)}], data.table(z
 test(2235.2, copy(DT)[, c("z", "x") := {list(2, NULL)}], data.table(z = 2))
 
 # move IDate from POSIXlt to C, add yearquarter; #649
-x = c("1111-11-11", "2019-01-01", "2019-02-28", "2019-03-01", "2019-12-31", "2020-02-29", "2020-03-01", "2020-12-31", "2040-01-01", "2040-12-31", "2100-03-01")
-test(2236.1, yday(x), c(315L, 1L, 59L, 60L, 365L, 60L, 61L, 366L, 1L, 366L, 60L))
-test(2236.2, mday(x), c(11L, 1L, 28L, 1L, 31L, 29L, 1L, 31L, 1L, 31L, 1L))
-test(2236.3, wday(x), c(7L, 3L, 5L, 6L, 3L, 7L, 1L, 5L, 1L, 2L, 2L))
-test(2236.4, week(x), c(46L, 1L, 9L, 9L, 53L, 9L, 9L, 53L, 1L, 53L, 9L))
-test(2236.5, month(x), c(11L, 1L, 2L, 3L, 12L, 2L, 3L, 12L, 1L, 12L, 3L))
-test(2236.6, quarter(x), c(4L, 1L, 1L, 1L, 4L, 1L, 1L, 4L, 1L, 4L, 1L))
-test(2236.7, year(x), c(1111L, 2019L, 2019L, 2019L, 2019L, 2020L, 2020L, 2020L, 2040L, 2040L, 2100L))
-test(2236.8, yearmon(x), c(1111+10/12, 2019, 2019+1/12, 2019+2/12, 2019+11/12, 2020+1/12, 2020+2/12, 2020+11/12, 2040, 2040+11/12, 2100+2/12))
-test(2236.9, yearqtr(x), c(1111.75, 2019, 2019, 2019, 2019.75, 2020, 2020, 2020.75, 2040, 2040.75, 2100))
+x = c("1111-11-11", "2019-01-01", "2019-02-28", "2019-03-01", "2019-12-31", "2020-02-29", "2020-03-01", "2020-12-31", "2040-01-01", "2040-12-31", "2100-03-01", NA)
+test(2236.1, yday(x), c(315L, 1L, 59L, 60L, 365L, 60L, 61L, 366L, 1L, 366L, 60L, NA))
+test(2236.2, mday(x), c(11L, 1L, 28L, 1L, 31L, 29L, 1L, 31L, 1L, 31L, 1L, NA))
+test(2236.3, wday(x), c(7L, 3L, 5L, 6L, 3L, 7L, 1L, 5L, 1L, 2L, 2L, NA))
+test(2236.4, week(x), c(46L, 1L, 9L, 9L, 53L, 9L, 9L, 53L, 1L, 53L, 9L, NA))
+test(2236.5, month(x), c(11L, 1L, 2L, 3L, 12L, 2L, 3L, 12L, 1L, 12L, 3L, NA))
+test(2236.6, quarter(x), c(4L, 1L, 1L, 1L, 4L, 1L, 1L, 4L, 1L, 4L, 1L, NA))
+test(2236.7, year(x), c(1111L, 2019L, 2019L, 2019L, 2019L, 2020L, 2020L, 2020L, 2040L, 2040L, 2100L, NA))
+test(2236.8, yearmon(x), c(1111+10/12, 2019, 2019+1/12, 2019+2/12, 2019+11/12, 2020+1/12, 2020+2/12, 2020+11/12, 2040, 2040+11/12, 2100+2/12, NA))
+test(2236.9, yearqtr(x), c(1111.75, 2019, 2019, 2019, 2019.75, 2020, 2020, 2020.75, 2040, 2040.75, 2100, NA))
 
 # as.data.table() no longer ignores row.names=, #5319
 dt = data.table(a=1:2, b=3:4)
diff --git a/src/idatetime.c b/src/idatetime.c
index c70df3b053..c25e9ec9c6 100644
--- a/src/idatetime.c
+++ b/src/idatetime.c
@@ -16,6 +16,12 @@ void convertSingleDate(int x, datetype type, void *out)
     static const char months[] = {31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31, 29};
     static const int quarter[] = {31, 91, 92, 92, 60};
 
+    if (x == NA_INTEGER) {
+        if (type == YEARMON || type == YEARQTR) *(double *)out = NA_REAL;
+        else *(int *)out = NA_INTEGER;
+        return;
+    }
+
     if (type == WDAY) {
         int wday = (x + 4) % 7;
         if (wday < 0) wday += 7;