diff --git a/table_test.go b/table_test.go
index 9cf0326..21e3b72 100644
--- a/table_test.go
+++ b/table_test.go
@@ -6,6 +6,7 @@ import (
 	"reflect"
 	"regexp"
 	"slices"
+	"strconv"
 	"strings"
 	"testing"
 )
@@ -783,6 +784,21 @@ func TestEveryUserAgentColumnAgreesWithItsString(t *testing.T) {
 	}
 }
 
+// TestEveryTimezoneRowIsWellFormed scans the file rather than drawing: the draw is
+// population-weighted, so it samples the populous head and leaves most rows unrendered.
+func TestEveryTimezoneRowIsWellFormed(t *testing.T) {
+	head, rows := shippedRows(t, "timezone.tsv", "offset", "territory", "weight", "zone")
+	offset := regexp.MustCompile(`^[+-](0\d|1[0-4]):[0-5]\d$`)
+	for i, r := range rows {
+		if !offset.MatchString(r[head["offset"]]) {
+			t.Errorf("timezone.tsv line %d: offset %q is no ±HH:MM", i+2, r[head["offset"]])
+		}
+		if w, err := strconv.Atoi(r[head["weight"]]); err != nil || w < 1 {
+			t.Errorf("timezone.tsv line %d: weight %q is not a positive number", i+2, r[head["weight"]])
+		}
+	}
+}
+
 // shippedRows reads a shipped misc TSV as the loader does, proving it names the
 // columns asked for and that every row fills them.
 func shippedRows(t *testing.T, file string, want ...string) (map[string]int, [][]string) {