diff --git a/test/test_composer_js_contracts.py b/test/test_composer_js_contracts.py
index eb08e0de..a4525f4c 100644
--- a/test/test_composer_js_contracts.py
+++ b/test/test_composer_js_contracts.py
@@ -185,3 +185,33 @@ def test_align_clears_the_anchor_and_moves_line_endpoints():
         "element resolves to the wrong edge"
     assert "el.x0" in body and "el.y0" in body, \
         "_alignElement no longer moves line endpoints"
+
+
+def test_divider_stroke_is_centered_in_led_pixels():
+    """A 0.5 canvas-pixel offset (correct only at SCALE=1) was applied after
+    scaling instead of before it, so at SCALE>1 the stroke bled into the
+    preceding LED row/column instead of straddling its own."""
+    body = _function_source(CANVAS, "_drawElement")
+    divider_branch = body[body.index("case 'divider'"):]
+    divider_branch = divider_branch[:divider_branch.index("case 'pips'")]
+    assert "ay * s + 0.5" not in divider_branch, \
+        "divider still offsets by 0.5 canvas pixels after scaling"
+    assert "ax * s + 0.5" not in divider_branch, \
+        "divider still offsets by 0.5 canvas pixels after scaling"
+    assert "(ay + 0.5) * s" in divider_branch and "(ax + 0.5) * s" in divider_branch, \
+        "divider stroke is not centered within its LED pixel"
+
+
+def test_gauge_radii_are_clamped_to_zero():
+    """An imported design can carry a small gauge with a wide lineWidth --
+    width=1, height=1, lineWidth=3 sends a negative radius into
+    ctx.ellipse(), which throws IndexSizeError and aborts render() for every
+    element still to be drawn, not just the gauge."""
+    body = _function_source(CANVAS, "_drawElement")
+    gauge_branch = body[body.index("case 'gauge'"):]
+    assert re.search(r"Math\.max\(0,\s*rx\s*-\s*lwPx\s*/\s*2\)", gauge_branch), \
+        "gauge x-radius is not clamped to zero"
+    assert re.search(r"Math\.max\(0,\s*ry\s*-\s*lwPx\s*/\s*2\)", gauge_branch), \
+        "gauge y-radius is not clamped to zero"
+    assert "rx - lwPx / 2" not in re.sub(r"Math\.max\(0,\s*rx\s*-\s*lwPx\s*/\s*2\)", "", gauge_branch), \
+        "an unclamped gauge radius is still passed to ctx.ellipse()"
diff --git a/web_interface/static/v3/js/composer/composer-canvas.js b/web_interface/static/v3/js/composer/composer-canvas.js
index c44940dc..05d6fc8c 100644
--- a/web_interface/static/v3/js/composer/composer-canvas.js
+++ b/web_interface/static/v3/js/composer/composer-canvas.js
@@ -486,11 +486,11 @@ window.ComposerCanvas = (() => {
           ctx.lineWidth = s;
           ctx.beginPath();
           if (isH) {
-            ctx.moveTo(0, ay * s + 0.5);
-            ctx.lineTo(_canvas.width, ay * s + 0.5);
+            ctx.moveTo(0, (ay + 0.5) * s);
+            ctx.lineTo(_canvas.width, (ay + 0.5) * s);
           } else {
-            ctx.moveTo(ax * s + 0.5, 0);
-            ctx.lineTo(ax * s + 0.5, _canvas.height);
+            ctx.moveTo((ax + 0.5) * s, 0);
+            ctx.lineTo((ax + 0.5) * s, _canvas.height);
           }
           ctx.stroke();
           break;
@@ -560,13 +560,17 @@ window.ComposerCanvas = (() => {
             ? Math.max(0, Math.min(100, parseFloat(pvGauge) || 0)) / 100
             : Math.max(0, Math.min(100, el.previewPct ?? 65)) / 100;
           const fillSweep = totalSweep * pct;
+          // A small imported gauge with a wide lineWidth would otherwise send
+          // a negative radius into ctx.ellipse(), which throws IndexSizeError
+          // and aborts the whole render() call.
+          const arx = Math.max(0, rx - lwPx / 2), ary = Math.max(0, ry - lwPx / 2);
           // biome-ignore lint/correctness/useQwikValidLexicalScope: not Qwik -- this is an Alpine.js component, and the rule is about Qwik's $() serialization boundary, which does not exist here.
           const toRad = deg => (deg - 90) * Math.PI / 180; // canvas 0=top, PIL 0=right → offset -90
 
           // Track arc
           if (el.hasTrack !== false) {
             ctx.beginPath();
-            ctx.ellipse(cx, cy, rx - lwPx / 2, ry - lwPx / 2, 0, toRad(startDeg), toRad(startDeg + totalSweep), false);
+            ctx.ellipse(cx, cy, arx, ary, 0, toRad(startDeg), toRad(startDeg + totalSweep), false);
             ctx.strokeStyle = `rgb(${el.trackR ?? 40},${el.trackG ?? 40},${el.trackB ?? 40})`;
             ctx.lineWidth = lwPx;
             ctx.stroke();
@@ -574,7 +578,7 @@ window.ComposerCanvas = (() => {
           // Fill arc
           if (pct > 0) {
             ctx.beginPath();
-            ctx.ellipse(cx, cy, rx - lwPx / 2, ry - lwPx / 2, 0, toRad(startDeg), toRad(startDeg + fillSweep), false);
+            ctx.ellipse(cx, cy, arx, ary, 0, toRad(startDeg), toRad(startDeg + fillSweep), false);
             ctx.strokeStyle = `rgb(${el.r},${el.g},${el.b})`;
             ctx.lineWidth = lwPx;
             ctx.stroke();