diff --git a/CHANGELOG.md b/CHANGELOG.md
index 638aae0..0cd8430 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,14 @@ and `MarkupString.Pueblo`. The packages share one version and are released toget
 The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and the project
 follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 2.24.2 — Unreleased
+
+### Fixed
+
+- **A table's heading rule matches its border**: unless a theme names its own, the line under a table's
+  headings is `─` (the default `LayoutTheme.Defaults.HeaderRule`), and `-` under an ASCII border or for an
+  ASCII reader. It was always `-`, so a table in a Unicode box had an ASCII rule under its headings.
+
 ## 2.24.1 — Unreleased
 
 ### Fixed
diff --git a/MarkupString.Tests/Layout/CompositionTests.cs b/MarkupString.Tests/Layout/CompositionTests.cs
index 2036c28..e003359 100644
--- a/MarkupString.Tests/Layout/CompositionTests.cs
+++ b/MarkupString.Tests/Layout/CompositionTests.cs
@@ -215,7 +215,7 @@ public async Task Shaded_Text_ColoursTheTextAndLeavesTheBoxDrawingInItsTheme()
 		var ansi = text.Render(MarkupFormat.Ansi, Registry);
 
 		await Assert.That(ansi).Contains("\u001b[38;2;0;128;0m|");
-		await Assert.That(ansi).Contains("\u001b[38;2;0;128;0m-");
+		await Assert.That(ansi).Contains("\u001b[38;2;0;128;0m─");
 		await Assert.That(ansi).Contains("\u001b[38;2;255;0;0mA");
 		await Assert.That(ansi).Contains("\u001b[38;2;0;0;255md");
 		await Assert.That(text.Runs.SelectMany(run => run.Markups).OfType<IDataMarkup>()).IsEmpty();
diff --git a/MarkupString.Tests/Layout/WidgetLayoutTests.cs b/MarkupString.Tests/Layout/WidgetLayoutTests.cs
index 09366b0..cd41c9b 100644
--- a/MarkupString.Tests/Layout/WidgetLayoutTests.cs
+++ b/MarkupString.Tests/Layout/WidgetLayoutTests.cs
@@ -112,6 +112,16 @@ public async Task Grid_InHtml_IsAColumnedList()
 		=> await Assert.That(BlockLayout.Build(new Grid(Names), 32).Render(MarkupFormat.Html, Registry))
 			.Contains("<ul class=\"ms-grid ms-down\" style=\"columns:8ch;column-gap:2ch\"><li>Mannaz</li>");
 
+	/// <summary>The rule under the headings is drawn like the border around it: <c>-</c> under an ASCII one or for an ASCII reader.</summary>
+	[Test]
+	public async Task Table_HeaderRule_FollowsTheBorder()
+	{
+		await Assert.That(Lines(Who(), 60)[1]).IsEqualTo(new string('─', 43));
+		await Assert.That(Lines(Who(), 60, Ascii)[1]).IsEqualTo(new string('-', 43));
+		await Assert.That(Lines(Who().Themed(new LayoutTheme { Border = BorderStyle.Ascii }), 60)[1]).IsEqualTo(new string('-', 43));
+		await Assert.That(Lines(Who().Themed(new LayoutTheme { Border = BorderStyle.Ascii, HeaderRule = P("=") }), 60)[1]).IsEqualTo(new string('=', 43));
+	}
+
 	private static Table Who(int nameMin = 6) => new(
 	[
 		new TableColumn(P("Name")) { Min = nameMin },
@@ -128,7 +138,7 @@ public async Task Table_ColumnsFitTheirWidestCell()
 		=> await Assert.That(Lines(Who(), 60)).IsEquivalentTo(new[]
 		{
 			"Name    Idle  Doing",
-			"-------------------------------------------",
+			"───────────────────────────────────────────",
 			"Mannaz    0s  Hooooo?",
 			"Raya      5m  Writing a scene in the garden",
 		});
@@ -138,7 +148,7 @@ public async Task Table_TooWide_WrapsFirst()
 		=> await Assert.That(Lines(Who(), 30)).IsEquivalentTo(new[]
 		{
 			"Name    Idle  Doing",
-			"------------------------------",
+			"──────────────────────────────",
 			"Mannaz    0s  Hooooo?",
 			"Raya      5m  Writing a scene",
 			"              in the garden",
@@ -149,7 +159,7 @@ public async Task Table_TooWideToWrap_LeavesOutTheLeastImportant()
 		=> await Assert.That(Lines(Who(), 18)).IsEquivalentTo(new[]
 		{
 			"Name    Idle",
-			"------------",
+			"────────────",
 			"Mannaz    0s",
 			"Raya      5m",
 		});
@@ -165,7 +175,7 @@ public async Task Table_NoColumnFits_RowsBecomeCards()
 
 	[Test]
 	public async Task Table_AColumnThatDoesNotWrap_IsWholeOrLeftOut()
-		=> await Assert.That(Lines(Who(), 10)).IsEquivalentTo(new[] { "Name", "------", "Mannaz", "Raya" });
+		=> await Assert.That(Lines(Who(), 10)).IsEquivalentTo(new[] { "Name", "──────", "Mannaz", "Raya" });
 
 	[Test]
 	public async Task Table_InHtml_IsATableThatDropsColumnsWhenNarrow()
@@ -218,7 +228,7 @@ public async Task Table_AColumnThatGrows_FillsTheWidth()
 	{
 		var lines = BlockLayout.Build(Growing(0, 1), 60).ToPlainText().Split('\n');
 
-		await Assert.That(lines[1]).IsEqualTo(new string('-', 60)).Because("the heading rule spans the table, which now spans its width");
+		await Assert.That(lines[1]).IsEqualTo(new string('─', 60)).Because("the heading rule spans the table, which now spans its width");
 		await Assert.That(lines[0].TrimEnd()).IsEqualTo("Name    Idle  Doing");
 		await Assert.That(lines[3].TrimEnd()).IsEqualTo("Raya      5m  Writing a scene in the garden");
 	}
@@ -233,7 +243,7 @@ public async Task Table_AGrowingColumn_StopsAtItsMax()
 	{
 		var table = Growing(0, 1) with { Columns = [.. Growing(0, 1).Columns.SetItem(2, Growing(0, 1).Columns[2] with { Max = 35 })] };
 
-		await Assert.That(Lines(table, 60)[1]).IsEqualTo(new string('-', 49)).Because("Doing grows from 29 to its 35 and no further");
+		await Assert.That(Lines(table, 60)[1]).IsEqualTo(new string('─', 49)).Because("Doing grows from 29 to its 35 and no further");
 	}
 
 	[Test]
diff --git a/MarkupString/Layout/Blocks/Block.cs b/MarkupString/Layout/Blocks/Block.cs
index bdf2cee..c29af25 100644
--- a/MarkupString/Layout/Blocks/Block.cs
+++ b/MarkupString/Layout/Blocks/Block.cs
@@ -261,7 +261,8 @@ public sealed record LayoutTheme
 
 	/// <summary>
 	/// What every unset piece ends up as: light box lines, light tree guides, <c>[█████░░░░░]</c>
-	/// gauges, <c>•</c> bullets, <c>": "</c> after a label and <c>-</c> under table headings.
+	/// gauges, <c>•</c> bullets, <c>": "</c> after a label and <c>─</c> under table headings (<c>-</c> under an
+	/// ASCII border).
 	/// </summary>
 	public static LayoutTheme Defaults { get; } = new()
 	{
@@ -273,7 +274,7 @@ public sealed record LayoutTheme
 		GaugeClose = MarkupText.Plain("]"),
 		Bullet = MarkupText.Plain("•"),
 		FieldSeparator = MarkupText.Plain(": "),
-		HeaderRule = MarkupText.Plain("-"),
+		HeaderRule = MarkupText.Plain("─"),
 	};
 
 	/// <summary>Boxes and rules.</summary>
diff --git a/MarkupString/Layout/Blocks/Table.cs b/MarkupString/Layout/Blocks/Table.cs
index 616bc28..5398b68 100644
--- a/MarkupString/Layout/Blocks/Table.cs
+++ b/MarkupString/Layout/Blocks/Table.cs
@@ -26,7 +26,10 @@ this with
 	/// <summary>Drawn between two columns on every line instead of the gap.</summary>
 	public MarkupText? Separator { get; init; }
 
-	/// <summary>The line under the headings, repeated; empty for none; unset, the theme's (<c>-</c>).</summary>
+	/// <summary>
+	/// The line under the headings, repeated; empty for none; unset, the theme's, or <c>─</c> (<c>-</c> under an
+	/// ASCII border) when the theme names none.
+	/// </summary>
 	public MarkupText? HeaderRule { get; init; }
 
 	/// <summary>
@@ -60,7 +63,7 @@ public override void Draw(LayoutContext context, int width, IList<MarkupText> li
 		MarkupText Join(IEnumerable<MarkupText> cells) => BlockText.Fit(MarkupText.Join(divider, cells), width);
 
 		lines.Add(Join(shown.Select(c => BlockText.Fit(context.Paint(theme => theme.HeadingColor, Columns[c].Header).FormatColumn(BlockText.Column(widths[c], Columns[c].Alignment))[0], widths[c]))));
-		var rule = HeaderRule ?? context.Theme.Piece(theme => theme.HeaderRule);
+		var rule = HeaderRule ?? context.Theme.HeaderRule ?? DefaultRule(context);
 		if (rule.Length > 0) lines.Add(BlockText.Fit(context.PaintLine(theme => theme.HeaderRuleColor, BlockText.Run(context.Glyph(rule, "-"), tableWidth)), width));
 
 		var cellLines = new List<MarkupText>[Columns.Length];
@@ -103,6 +106,10 @@ public override void DrawLinear(LayoutContext context, int width, IList<MarkupTe
 		}
 	}
 
+	/// <summary>The default rule under the headings, ASCII when the border it sits among is.</summary>
+	private static MarkupText DefaultRule(LayoutContext context) =>
+		context.Border(null).IsAscii ? MarkupText.Plain("-") : LayoutTheme.Defaults.HeaderRule!;
+
 	/// <summary>Each row as a card of labelled values, the way a phone shows a table too wide for it.</summary>
 	private void DrawCards(LayoutContext context, int width, IList<MarkupText> lines)
 	{
diff --git a/docs/layout.md b/docs/layout.md
index f51b770..cb81e6f 100644
--- a/docs/layout.md
+++ b/docs/layout.md
@@ -475,12 +475,13 @@ widest cell. When the table is too wide, the columns that wrap give way, widest
 least width; then the column with the highest `Priority` number is left out, and so on. A column that
 does not wrap is shown whole or not at all. When not even the most important column fits, each row
 becomes a card of labelled values. In HTML, a column of priority 2 carries `ms-p2` and one of 3 or
-more `ms-p3`, which `LayoutCss.Fixed` hides on narrow pages.
+more `ms-p3`, which `LayoutCss.Fixed` hides on narrow pages. The rule under the headings is the
+theme's `HeaderRule`, or `─` when it names none (`-` under an ASCII border or for an ASCII reader).
 
 ```
 At 30:                            At 18:
 Name    Idle  Doing               Name    Idle
-------------------------------    ------------
+──────────────────────────────    ────────────
 Mannaz    0s  Hooooo?             Mannaz    0s
 Raya      5m  Writing a scene     Raya      5m
               in the garden