diff --git a/R/sql-expr.R b/R/sql-expr.R
index ea935367d..45501e6ff 100644
--- a/R/sql-expr.R
+++ b/R/sql-expr.R
@@ -47,7 +47,9 @@ sql_call2 <- function(.fn, ..., con = sql_current_con()) {
 
 
 replace_expr <- function(x, con) {
-  if (is.atomic(x) || blob::is_blob(x)) {
+  if (is.null(x)) {
+    "NULL"
+  } else if (is.atomic(x) || blob::is_blob(x)) {
     as.character(escape(unname(x), con = con))
   } else if (is.name(x)) {
     as.character(x)
diff --git a/R/translate-sql-window.R b/R/translate-sql-window.R
index 8cf9dc40c..aa01d6b70 100644
--- a/R/translate-sql-window.R
+++ b/R/translate-sql-window.R
@@ -454,7 +454,7 @@ translate_window_where_all <- function(x, window_funs = common_window_funs()) {
 }
 
 window_where <- function(expr, comp) {
-  stopifnot(is.call(expr) || is.name(expr) || is.atomic(expr))
+  stopifnot(is.call(expr) || is.name(expr) || is.atomic(expr) || is.null(expr))
   check_list(comp)
 
   list(
diff --git a/tests/testthat/test-sql-expr.R b/tests/testthat/test-sql-expr.R
index a51657934..88e26a252 100644
--- a/tests/testthat/test-sql-expr.R
+++ b/tests/testthat/test-sql-expr.R
@@ -1,3 +1,8 @@
+test_that("NULL becomes SQL NULL", {
+  con <- simulate_dbi()
+  expect_equal(sql_expr(NULL), sql("NULL"))
+})
+
 test_that("atomic vectors are escaped", {
   con <- simulate_dbi()