diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index c349b99daf..6255f4f843 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -18249,3 +18249,16 @@ DT = data.table(A=letters[1:3])
 test(2219.1, DT[2, A:=as.IDate("2021-02-03")],                              data.table(A=c("a","2021-02-03","c")))
 if (test_bit64) test(2219.2, DT[3, A:=as.integer64("4611686018427387906")], data.table(A=c("a","2021-02-03","4611686018427387906")))
 
+# gforce improve coverage
+DT = data.table(g=1:2, i=c(NA, 1:4, NA), f=factor(letters[1:6]), l=as.list(1:6))
+options(datatable.optimize = 2L)
+funs = c("sum", "mean", "min", "max", "median", "var", "sd", "prod")
+testnum = 2220
+for (fun in funs) {
+  testnum = testnum + 0.01
+  test(testnum, EVAL("DT[,",fun,"(i, na.rm='a'), g]"), error="na.rm must be TRUE or FALSE")
+  testnum = testnum + 0.01
+  test(testnum, EVAL("DT[,",fun,"(f), g]"), error=sprintf("%s is not meaningful for factors.", fun))
+}
+test(testnum+0.01, DT[, prod(l), g], error="GForce prod can only be applied to columns, not .SD or similar.")
+
diff --git a/src/gsumm.c b/src/gsumm.c
index be3b0f7855..5bb2620243 100644
--- a/src/gsumm.c
+++ b/src/gsumm.c
@@ -348,8 +348,7 @@ SEXP gsum(SEXP x, SEXP narmArg)
   double started = wallclock();
   const bool verbose=GetVerbose();
   if (verbose) Rprintf(_("This gsum (narm=%s) took ... "), narm?"TRUE":"FALSE");
-  if (nrow != n)
-    error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gsum");
+  if (nrow != n) error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gsum");
   bool anyNA=false;
   SEXP ans;
   switch(TYPEOF(x)) {
@@ -729,8 +728,7 @@ static SEXP gminmax(SEXP x, SEXP narm, const bool min)
   const int n = nosubset ? length(x) : irowslen;
   //clock_t start = clock();
   SEXP ans;
-  if (nrow != n)
-    error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gminmax");
+  if (nrow != n) error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gminmax");
   // GForce guarantees each group has at least one value; i.e. we don't need to consider length-0 per group here
   switch(TYPEOF(x)) {
   case LGLSXP: case INTSXP: {
@@ -865,8 +863,7 @@ SEXP gmedian(SEXP x, SEXP narmArg) {
     error(_("%s is not meaningful for factors."), "median");
   const bool isInt64 = INHERITS(x, char_integer64), narm = LOGICAL(narmArg)[0];
   const int n = (irowslen == -1) ? length(x) : irowslen;
-  if (nrow != n)
-    error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gmedian");
+  if (nrow != n) error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gmedian");
   SEXP ans = PROTECT(allocVector(REALSXP, ngrp));
   double *ansd = REAL(ans);
   const bool nosubset = irowslen==-1;
@@ -1021,8 +1018,7 @@ static SEXP gvarsd1(SEXP x, SEXP narmArg, bool isSD)
   if (inherits(x, "factor"))
     error(_("%s is not meaningful for factors."), isSD ? "sd" : "var");
   const int n = (irowslen == -1) ? length(x) : irowslen;
-  if (nrow != n)
-    error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gvar");
+  if (nrow != n) error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gvar");
   SEXP sub, ans = PROTECT(allocVector(REALSXP, ngrp));
   double *ansd = REAL(ans);
   const bool nosubset = irowslen==-1;
@@ -1119,8 +1115,7 @@ SEXP gprod(SEXP x, SEXP narmArg) {
   const int n = nosubset ? length(x) : irowslen;
   //clock_t start = clock();
   SEXP ans;
-  if (nrow != n)
-    error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gprod");
+  if (nrow != n) error(_("nrow [%d] != length(x) [%d] in %s"), nrow, n, "gprod");
   long double *s = malloc(ngrp * sizeof(long double));
   if (!s) error(_("Unable to allocate %d * %d bytes for gprod"), ngrp, sizeof(long double));
   for (int i=0; i<ngrp; ++i) s[i] = 1.0;