diff --git a/frontend/src/__tests__/pin-inspector-layout.test.ts b/frontend/src/__tests__/pin-inspector-layout.test.ts
index f9d86985..2b7a11da 100644
--- a/frontend/src/__tests__/pin-inspector-layout.test.ts
+++ b/frontend/src/__tests__/pin-inspector-layout.test.ts
@@ -206,6 +206,67 @@ describe('layoutInspectorPins — inset columns (the ReSpeaker Lite case)', () =
   });
 });
 
+
+describe('layoutInspectorPins — the Arduino Uno (two opposite headers)', () => {
+  // node_modules/@wokwi/elements arduino-uno-element pinInfo, board 274x208.
+  // 18 pins along the top header (y=9) and 13 along the bottom (y=192), with
+  // SIX x values shared between the two. Reading those pairs as columns threw
+  // most of the board into the side gutters with leaders fanning across the
+  // art; a column has to be a run of pads, not two opposite ends.
+  const UNO: InspectorPinInput[] = [
+    { name: 'A5.2', x: 87, y: 9 },
+    { name: 'A4.2', x: 97, y: 9 },
+    { name: 'AREF', x: 106, y: 9 },
+    { name: 'GND.1', x: 115.5, y: 9 },
+    { name: '13', x: 125, y: 9 },
+    { name: '12', x: 134.5, y: 9 },
+    { name: '11', x: 144, y: 9 },
+    { name: '10', x: 153.5, y: 9 },
+    { name: '9', x: 163, y: 9 },
+    { name: '8', x: 173, y: 9 },
+    { name: '7', x: 189, y: 9 },
+    { name: '6', x: 198.5, y: 9 },
+    { name: '5', x: 208, y: 9 },
+    { name: '4', x: 217.5, y: 9 },
+    { name: '3', x: 227, y: 9 },
+    { name: '2', x: 236.5, y: 9 },
+    { name: '1', x: 246, y: 9 },
+    { name: '0', x: 255.5, y: 9 },
+    { name: 'IOREF', x: 131, y: 191.5 },
+    { name: 'RESET', x: 140.5, y: 191.5 },
+    { name: '3.3V', x: 150, y: 191.5 },
+    { name: '5V', x: 160, y: 191.5 },
+    { name: 'GND.2', x: 169.5, y: 191.5 },
+    { name: 'GND.3', x: 179, y: 191.5 },
+    { name: 'VIN', x: 188.5, y: 191.5 },
+    { name: 'A0', x: 208, y: 191.5 },
+    { name: 'A1', x: 217.5, y: 191.5 },
+    { name: 'A2', x: 227, y: 191.5 },
+    { name: 'A3', x: 236.5, y: 191.5 },
+    { name: 'A4', x: 246, y: 191.5 },
+    { name: 'A5', x: 255.5, y: 191.5 }
+  ];
+
+  const r = layoutInspectorPins(UNO, { width: 274, height: 208 });
+
+  it('puts every pin on the header it belongs to', () => {
+    expect(r.pins).toHaveLength(31);
+    expect(r.pins.filter((p) => p.edge === 'top')).toHaveLength(18);
+    expect(r.pins.filter((p) => p.edge === 'bottom')).toHaveLength(13);
+  });
+
+  it('uses no side gutters at all', () => {
+    expect(r.pins.some((p) => p.edge === 'left' || p.edge === 'right')).toBe(false);
+  });
+
+  it('keeps the shared-x pairs apart — one per header', () => {
+    for (const name of ['5', '4', '3', '2', '1', '0']) {
+      const p = r.pins.find((q) => q.name === name);
+      if (p) expect(p.edge).toBe('top');
+    }
+  });
+});
+
 describe('signalKindOf', () => {
   it('maps the wokwi signal shapes', () => {
     expect(signalKindOf({ name: 'SDA', x: 0, y: 0, signals: [{ type: 'i2c', signal: 'SDA' }] })).toBe('i2c');
diff --git a/frontend/src/utils/pinInspectorLayout.ts b/frontend/src/utils/pinInspectorLayout.ts
index 5ae3603c..a60d9ffd 100644
--- a/frontend/src/utils/pinInspectorLayout.ts
+++ b/frontend/src/utils/pinInspectorLayout.ts
@@ -187,12 +187,25 @@ export function layoutInspectorPins(
   const ys = pins.map((p) => p.y * scale);
   const side = new Array<PinEdge | null>(pins.length).fill(null);
 
+  /** Largest gap between consecutive values — a real header has small ones. */
+  const maxGap = (vals: number[]): number => {
+    const s = [...vals].sort((a, b) => a - b);
+    let m = 0;
+    for (let i = 1; i < s.length; i++) m = Math.max(m, s[i] - s[i - 1]);
+    return m;
+  };
+
   // Vertical columns win first: they are the dominant shape on breakout
-  // boards, shields and every DIP part.
+  // boards, shields and every DIP part. A column must be a RUN of pads, which
+  // is why it needs three of them and small gaps: an Arduino Uno has two
+  // opposite headers with six x values shared between them, and reading those
+  // pairs as columns threw most of the board's pins into the side gutters
+  // with a fan of leader lines across the art.
   for (const g of cluster(xs)) {
-    if (g.length < 2) continue;
-    const spanY = Math.max(...g.map((i) => ys[i])) - Math.min(...g.map((i) => ys[i]));
-    if (spanY < TOL) continue; // that is a row, not a column
+    if (g.length < 3) continue;
+    const gys = g.map((i) => ys[i]);
+    if (Math.max(...gys) - Math.min(...gys) < TOL) continue; // a row, not a column
+    if (maxGap(gys) > 0.4 * H) continue; // opposite ends of the body, not a run
     const cx = g.reduce((s, i) => s + xs[i], 0) / g.length;
     const e: PinEdge = cx <= W / 2 ? 'left' : 'right';
     for (const i of g) side[i] = e;
@@ -201,8 +214,9 @@ export function layoutInspectorPins(
   for (const g of cluster(ys)) {
     const free = g.filter((i) => side[i] === null);
     if (free.length < 2) continue;
-    const spanX = Math.max(...free.map((i) => xs[i])) - Math.min(...free.map((i) => xs[i]));
-    if (spanX < TOL) continue;
+    const gxs = free.map((i) => xs[i]);
+    if (Math.max(...gxs) - Math.min(...gxs) < TOL) continue;
+    if (maxGap(gxs) > 0.4 * W) continue;
     const cy = free.reduce((s, i) => s + ys[i], 0) / free.length;
     const e: PinEdge = cy <= H / 2 ? 'top' : 'bottom';
     for (const i of free) side[i] = e;