diff --git a/calc_test.go b/calc_test.go
index 2efdf89..77adf77 100644
--- a/calc_test.go
+++ b/calc_test.go
@@ -247,11 +247,21 @@ func TestCalcOverANeverNumericOperandIsRejected(t *testing.T) {
 }
 
 func TestCalcConstantZeroDivisorIsRejected(t *testing.T) {
-	for _, bad := range []string{`"{calc(1/0)}"`, `"{calc(2/(1-1))}"`, `{"format":"{calc(x/y)}","x":"1","y":"0"}`, `{"format":"{calc(x/(y*2))}","x":"1","y":" 0 "}`} {
-		if _, err := compile(parse(t, bad)); err == nil || !strings.Contains(err.Error(), "zero") {
-			t.Errorf("compile(%s) = %v, want the constant zero divisor rejected", bad, err)
+	for src, want := range map[string]string{
+		`"{calc(1/0)}"`:                                  "divides by 0",
+		`"{calc(2/(1-1))}"`:                              "divides by (1 - 1)",
+		`{"format":"{calc(x/y)}","x":"1","y":"0"}`:       "divides by y",
+		`{"format":"{calc(x/(y*2))}","x":"1","y":" 0 "}`: "divides by (y * 2)",
+		`{"format":"{calc((a/0)+b)}","a":"1","b":"2"}`:   "divides by 0",
+		`{"format":"{calc(a/-0)}","a":"1"}`:              "divides by -0",
+	} {
+		if _, err := compile(parse(t, src)); err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("compile(%s) = %v, want the constant zero divisor rejected naming %q", src, err, want)
 		}
 	}
+	if _, err := compile(parse(t, `{"format":"{calc(a/(b*c))}","a":"1","b":"0","c":["1","2"]}`)); err != nil {
+		t.Errorf("compile(a/(b*c)) = %v, want a divisor that varies accepted", err)
+	}
 	f := engine(1)
 	for i := 0; i < 50; i++ {
 		if got := mustRender(t, f, `{"format":"{calc(x/y)}","x":"1","y":["0","1"]}`); got == "+Inf" {
diff --git a/cmd/fejkdata/main_test.go b/cmd/fejkdata/main_test.go
index cb08507..acc5a23 100644
--- a/cmd/fejkdata/main_test.go
+++ b/cmd/fejkdata/main_test.go
@@ -362,3 +362,11 @@ func TestRunEmptyDataPathIsNamed(t *testing.T) {
 		t.Errorf("run(--data-path=) = %d, %q, want the empty path named", code, errb)
 	}
 }
+
+func TestRunNumbersFollowTheShell(t *testing.T) {
+	_, want, _ := runOut("--seed", "7", "--repeat", "3", "sv_SE.word")
+	code, got, errb := runOut("--seed", "007", "--repeat", "+3", "sv_SE.word")
+	if code != 0 || got != want {
+		t.Errorf("run(--seed 007 --repeat +3) = %d, %q, stderr %q; want the same as --seed 7 --repeat 3 %q", code, got, errb, want)
+	}
+}
diff --git a/template_test.go b/template_test.go
index d5aa2ad..74dbc30 100644
--- a/template_test.go
+++ b/template_test.go
@@ -365,3 +365,17 @@ func TestAlternationThreeWay(t *testing.T) {
 		t.Fatalf("3-way alternation produced %v, want A, B and C", seen)
 	}
 }
+
+func TestArgErrorsNameTheSpelling(t *testing.T) {
+	for src, want := range map[string]string{
+		`"{float(1,2,02)}"`:                 "write 2",
+		`{"format":"{calc(a,02)}","a":"1"}`: "write 2",
+		`"{digits(+5)}"`:                    "write 5",
+		`"{hex(99999999999999999999)}"`:     "exceeds the maximum",
+		`"{int(007,9)}"`:                    "write 7",
+	} {
+		if _, err := compile(parse(t, src)); err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("compile(%s) = %v, want an error saying %q", src, err, want)
+		}
+	}
+}