diff --git a/src/group_indices.cpp b/src/group_indices.cpp
index a9427d9414..9e632e85a8 100644
--- a/src/group_indices.cpp
+++ b/src/group_indices.cpp
@@ -247,13 +247,13 @@ class FactorSlicer : public Slicer {
       int idx = range[i];
       int value = f[idx];
 
-      // will support it later
-      if (value == NA_INTEGER) stop("NA not supported");
+      if (value == NA_INTEGER) {
+        bad_col(visitors.name(depth), "contains implicit missing values. Consider `forcats::fct_explicit_na` to turn them explicit");
+      }
       indices[value - 1].push_back(idx);
     }
   }
 
-
   int depth;
 
   const std::vector<SEXP>& data;
diff --git a/tests/testthat/test-group-by.r b/tests/testthat/test-group-by.r
index 7d05772da4..5274b00330 100644
--- a/tests/testthat/test-group-by.r
+++ b/tests/testthat/test-group-by.r
@@ -70,9 +70,8 @@ test_that("group_by uses shallow copy", {
 })
 
 test_that("FactorVisitor handles NA. #183", {
-  skip("until we can group again by a factor that has NA")
-  g <- group_by(MASS::survey, M.I)
-  expect_equal(g$M.I, MASS::survey$M.I)
+  d <- data.frame(x = 1:3, f = factor(c("a", "b", NA)))
+  expect_error(group_by(d, f), "Column `f` contains implicit missing values")
 })
 
 test_that("group_by orders by groups. #242", {