diff --git a/src/assign.c b/src/assign.c
index 57f0e6eb9b..76708486e9 100644
--- a/src/assign.c
+++ b/src/assign.c
@@ -182,9 +182,7 @@ SEXP alloccol(SEXP dt, R_len_t n, Rboolean verbose)
   if (isNull(klass)) error(_("dt passed to alloccol has no class attribute. Please report result of traceback() to data.table issue tracker."));
   const R_len_t l = LENGTH(dt);
   SEXP names = getAttrib(dt,R_NamesSymbol);
-  // names may be NULL when null.data.table() passes list() to alloccol for example.
-  // So, careful to use length() on names, not LENGTH().
-  if (length(names)!=l) internal_error(__func__, "length of names (%d) is not length of dt (%d)", length(names),l); // # nocov
+  if (LENGTH(names)!=l) internal_error(__func__, "length of names (%d) is not length of dt (%d)", LENGTH(names),l); // # nocov
   if (!selfrefok(dt,verbose))
     return shallow(dt,R_NilValue,(n>l) ? n : l);  // e.g. test 848 and 851 in R > 3.0.2
     // added (n>l) ? ... for #970, see test 1481.
diff --git a/src/dogroups.c b/src/dogroups.c
index 5a677c9cd2..5e88a190e3 100644
--- a/src/dogroups.c
+++ b/src/dogroups.c
@@ -43,7 +43,6 @@ static bool anySpecialStatic(SEXP x, hashtab * specials) {
   // we restore the true truelength for when R starts to use vector truelength.
   SEXP list_el;
   const int n = length(x);
-  // use length() not LENGTH() because isNewList() is true for NULL
   if (n==0)
     return false;
   if (isVectorAtomic(x))
@@ -362,7 +361,7 @@ SEXP dogroups(SEXP dt, SEXP dtcols, SEXP groups, SEXP grpcols, SEXP jiscols, SEX
     if (njval==0) njval = LENGTH(jval);   // for first group, then the rest (when non 0) must conform to the first >0 group
     if (njval!=LENGTH(jval)) error(_("j doesn't evaluate to the same number of columns for each group"));  // this would be a problem even if we unlisted afterwards. This way the user finds out earlier though so he can fix and rerun sooner.
     for (int j=0; j<njval; ++j) {
-      int k = length(VECTOR_ELT(jval,j));  // might be NULL, so length not LENGTH
+      int k = length(VECTOR_ELT(jval,j));
       maxn = k>maxn ? k : maxn;
     }
     if (ansloc + maxn > estn) {