diff --git a/OpenNest.Core/Diagnostics/OverlapMaterial.cs b/OpenNest.Core/Diagnostics/OverlapMaterial.cs
index 37f6615..94651f2 100644
--- a/OpenNest.Core/Diagnostics/OverlapMaterial.cs
+++ b/OpenNest.Core/Diagnostics/OverlapMaterial.cs
@@ -10,7 +10,13 @@ namespace OpenNest.Diagnostics;
 /// <summary>Request-local, validated single-outer material. Never exposed to report consumers.</summary>
 internal sealed record OverlapMaterial(Polygon Outer, List<Polygon> Holes)
 {
-    internal static OverlapMaterial Read(List<Entity> entities, CancellationToken cancellationToken)
+    internal static OverlapMaterial Read(List<Entity> entities, CancellationToken cancellationToken) =>
+        Read(entities, cancellationToken, PlateOverlapAnalyzer.ChordTolerance);
+
+    /// <summary>As <see cref="Read(List{Entity}, CancellationToken)"/> with a caller-chosen
+    /// chord tolerance (a finer one for keep-outs smaller than the default).</summary>
+    internal static OverlapMaterial Read(List<Entity> entities, CancellationToken cancellationToken,
+        double chordTolerance)
     {
         // ShapeBuilder can reverse entities while chaining. Own a fresh copy for each analysis.
         var shapes = ShapeBuilder.GetShapes(entities.Select(entity => entity.Clone()));
@@ -21,7 +27,7 @@ internal sealed record OverlapMaterial(Polygon Outer, List<Polygon> Holes)
         {
             cancellationToken.ThrowIfCancellationRequested();
             ValidateChain(shape);
-            var polygon = shape.ToPolygonWithTolerance(PlateOverlapAnalyzer.ChordTolerance);
+            var polygon = shape.ToPolygonWithTolerance(chordTolerance);
             // The analytic chain was validated above. Normalize its sampled seam (e.g.
             // sin(2*pi) is not exactly zero), rather than adding a spurious microscopic edge.
             if (polygon.IsClosed())
diff --git a/OpenNest.Core/Diagnostics/PlateOverlapAnalyzer.cs b/OpenNest.Core/Diagnostics/PlateOverlapAnalyzer.cs
index 4f65e86..0ecbf76 100644
--- a/OpenNest.Core/Diagnostics/PlateOverlapAnalyzer.cs
+++ b/OpenNest.Core/Diagnostics/PlateOverlapAnalyzer.cs
@@ -280,7 +280,12 @@ public static class PlateOverlapAnalyzer
                     // (negligibly small) clamp rectangle as the overlap fragment.
                     if (KeepOutOverlap.NeedsToleranceFreeTest(zone))
                     {
-                        if (KeepOutOverlap.MaterialEnters(part.Material.Outer, part.Material.Holes, zone))
+                        // Re-read the native contours flattened finely enough for this clamp:
+                        // the shared 0.001 chords can hide material between an arc and its chord.
+                        var fine = OverlapMaterial
+                            .Read(part.Input.Source.Entities, cancellationToken, KeepOutOverlap.FlatteningTolerance(zone))
+                            .Transform(part.Input.Rotation, part.Input.Location);
+                        if (KeepOutOverlap.MaterialEnters(fine.Outer, fine.Holes, zone))
                             findings.Add(TinyClampFinding(part, clamp));
                         continue;
                     }
diff --git a/OpenNest.Core/Geometry/KeepOutOverlap.cs b/OpenNest.Core/Geometry/KeepOutOverlap.cs
index 54ecce8..d6e0c65 100644
--- a/OpenNest.Core/Geometry/KeepOutOverlap.cs
+++ b/OpenNest.Core/Geometry/KeepOutOverlap.cs
@@ -19,6 +19,35 @@ public static class KeepOutOverlap
     public static bool NeedsToleranceFreeTest(Box keepOut) =>
         keepOut.Length < ToleranceFreeBelow || keepOut.Width < ToleranceFreeBelow;
 
+    /// <summary>
+    /// Chord tolerance for flattening real part material against <paramref name="keepOut"/>:
+    /// a quarter of its smaller side (at most <see cref="ToleranceFreeBelow"/>), so the
+    /// sliver between an arc and its chord can never hold the whole rectangle - any real
+    /// overlap then shows up as a polygon edge through it or its centre inside.
+    /// </summary>
+    public static double FlatteningTolerance(Box keepOut) =>
+        System.Math.Min(ToleranceFreeBelow, System.Math.Min(keepOut.Length, keepOut.Width) / 4);
+
+    /// <summary>
+    /// <see cref="MaterialEnters"/> for a part's native contours (lines kept exactly, arcs
+    /// flattened at <see cref="FlatteningTolerance"/>), translated by <paramref name="offset"/>.
+    /// Never fed through a grid-rounding offset or a coarse flattening.
+    /// </summary>
+    public static bool ProfileEnters(ShapeProfile profile, Vector offset, Box keepOut)
+    {
+        var tolerance = FlatteningTolerance(keepOut);
+        var perimeter = profile.Perimeter.ToPolygonWithTolerance(tolerance);
+        perimeter.Offset(offset);
+        var holes = new List<Polygon>(profile.Cutouts.Count);
+        foreach (var cutout in profile.Cutouts)
+        {
+            var hole = cutout.ToPolygonWithTolerance(tolerance);
+            hole.Offset(offset);
+            holes.Add(hole);
+        }
+        return MaterialEnters(perimeter, holes, keepOut);
+    }
+
     /// <summary>
     /// True when the material (perimeter minus holes) shares positive area with the open
     /// rectangle: some boundary edge runs through its interior, or its interior lies wholly
diff --git a/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs b/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs
index b003d98..e444758 100644
--- a/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs
+++ b/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs
@@ -186,4 +186,74 @@ public class TinyClampZoneTests
 
         Assert.False(EntersTinyZone(mover), $"pushed to ({mover.Location.X:R},{mover.Location.Y:R})");
     }
+    // PM 407f5eb7: the tolerance-free test must read the part's real material, not the
+    // 1e-4-grid validation outline or a 0.001 arc flattening.
+    private static Program RectProgram(double w, double h)
+    {
+        var program = new Program();
+        program.MoveTo(0, 0);
+        program.LineTo(w, 0);
+        program.LineTo(w, h);
+        program.LineTo(0, h);
+        program.LineTo(0, 0);
+        return program;
+    }
+
+    private static Program DiskProgram()
+    {
+        // Radius 2 centred at (10, 10), two absolute CCW half circles.
+        var program = new Program();
+        program.MoveTo(12, 10);
+        program.ArcTo(8, 10, 10, 10, RotationType.CCW);
+        program.ArcTo(12, 10, 10, 10, RotationType.CCW);
+        return program;
+    }
+
+    private static Box DiskBox(double radius)
+    {
+        var cx = 10 + radius * System.Math.Cos(0.02);
+        var cy = 10 + radius * System.Math.Sin(0.02);
+        return new Box(cx - 0.000005, cy - 0.000005, Tiny, Tiny);
+    }
+
+    public static TheoryData<string, Box, bool> RealMaterialRows => new()
+    {
+        { "rect-8.00004", new Box(8.00002, 0.5, Tiny, Tiny), true },   // wholly inside the part
+        { "rect-8.00004", new Box(8.00005, 0.5, Tiny, Tiny), false },  // just beyond its edge
+        { "rect-2.00004", new Box(2.000032, 1, 5e-6, Tiny), true },
+        { "disk", DiskBox(1.9998), true },  // inside the true arc, outside its 0.001 chords
+        { "disk", DiskBox(2.0002), false }, // just outside the true arc
+    };
+
+    private static Program MaterialProgram(string name) => name switch
+    {
+        "rect-8.00004" => RectProgram(8.00004, 2),
+        "rect-2.00004" => RectProgram(2.00004, 2),
+        _ => DiskProgram(),
+    };
+
+    [Theory]
+    [MemberData(nameof(RealMaterialRows))]
+    public void LayoutCheckReadsRealMaterialAroundATinyClamp(string material, Box zone, bool overlaps)
+    {
+        var program = MaterialProgram(material);
+        var stock = new NestPlateStock("sheet", new Size(20, 20), null, 0, default, 1,
+            new[] { new ClampZone("tiny", zone) });
+        var job = new NestJob(new[] { new NestJobPart("p", PartGeometrySnapshot.FromProgram(program), 1, 0,
+            RotationPolicy.Fixed(0)) }, new[] { stock });
+        NestJobValidator.Validate(job);
+        var result = new NestJobResult(NestJobStatus.Complete, NestJobStopReason.Completed,
+            new[] { new NestJobPlateResult(0, stock, new[] { new NestJobPlacement("p", 0, 0, 0, 0) }) },
+            Array.Empty<PartFulfillment>(), Array.Empty<StockUsage>());
+
+        Assert.Equal(overlaps, ClampViolations(job, result).Count > 0);
+    }
+
+    [Theory]
+    [MemberData(nameof(RealMaterialRows))]
+    public void InteractiveKeepOutTestReadsRealMaterial(string material, Box zone, bool overlaps)
+    {
+        var part = new Part(new Drawing(material, MaterialProgram(material)));
+        Assert.Equal(overlaps, InteractiveClamps.MaterialInKeepOut(part, zone));
+    }
 }
diff --git a/OpenNest.Engine/Jobs/InteractiveClamps.cs b/OpenNest.Engine/Jobs/InteractiveClamps.cs
index 233e74b..525de3c 100644
--- a/OpenNest.Engine/Jobs/InteractiveClamps.cs
+++ b/OpenNest.Engine/Jobs/InteractiveClamps.cs
@@ -100,8 +100,7 @@ internal static class InteractiveClamps
         // A keep-out below the polygon tolerance collapses in the tolerant test and would
         // read as clear (PM b0062c73); judge it tolerance-free instead.
         if (KeepOutOverlap.NeedsToleranceFreeTest(keepOut))
-            return KeepOutOverlap.MaterialEnters(partProfile.Perimeter.ToPolygonWithTolerance(0.001),
-                HolePolygons(partProfile), keepOut);
+            return KeepOutOverlap.ProfileEnters(partProfile, new Vector(0, 0), keepOut);
         var zoneProfile = new ShapeProfile(RectangleEntities(keepOut));
         if (zoneProfile.Perimeter == null)
             return true;
diff --git a/OpenNest.Engine/Jobs/NestLayoutCheck.cs b/OpenNest.Engine/Jobs/NestLayoutCheck.cs
index 5bd6ddd..aa08d62 100644
--- a/OpenNest.Engine/Jobs/NestLayoutCheck.cs
+++ b/OpenNest.Engine/Jobs/NestLayoutCheck.cs
@@ -186,8 +186,7 @@ public static class NestLayoutCheck
                 if (!BoxesTouch(keepOut, MaterialBounds(part)))
                     continue;
 
-                var material = Outline(part, 0);
-                if (material == null || !OverlapsKeepOut(material, keepOutOutline, keepOut))
+                if (!OverlapsKeepOut(part, keepOutOutline, keepOut))
                     continue;
 
                 result.Add(
@@ -218,13 +217,21 @@ public static class NestLayoutCheck
     /// <summary>
     /// Material against a keep-out rectangle. A rectangle below the outline tolerance, or one
     /// the triangulated test cannot prepare, is judged by the tolerance-free rectangle test
-    /// instead: the tolerant path would call real overlap clear.
+    /// on the part's native contours (not the grid-rounded validation outline): the
+    /// tolerant path would call real overlap clear. A part without material is skipped.
     /// </summary>
-    private static bool OverlapsKeepOut(PartOutline material, PartOutline keepOutOutline, Box keepOut)
+    private static bool OverlapsKeepOut(Part part, PartOutline keepOutOutline, Box keepOut)
     {
         if (KeepOutOverlap.NeedsToleranceFreeTest(keepOut) || keepOutOutline.Triangles == null)
-            return KeepOutOverlap.MaterialEnters(material.Perimeter, material.Holes, keepOut);
-        return Overlaps(material, keepOutOutline);
+        {
+            var entities = ConvertProgram.ToGeometry(part.Program)
+                .Where(e => SpecialLayers.IsMaterial(e.Layer))
+                .ToList();
+            var profile = entities.Count == 0 ? null : new ShapeProfile(entities);
+            return profile?.Perimeter != null && KeepOutOverlap.ProfileEnters(profile, part.Location, keepOut);
+        }
+        var material = Outline(part, 0);
+        return material != null && Overlaps(material, keepOutOutline);
     }
 
     /// <summary>
diff --git a/OpenNest.Tests/Diagnostics/PlateOverlapAnalyzerClampZoneTests.cs b/OpenNest.Tests/Diagnostics/PlateOverlapAnalyzerClampZoneTests.cs
index 461d44e..e49e35b 100644
--- a/OpenNest.Tests/Diagnostics/PlateOverlapAnalyzerClampZoneTests.cs
+++ b/OpenNest.Tests/Diagnostics/PlateOverlapAnalyzerClampZoneTests.cs
@@ -214,6 +214,40 @@ public class PlateOverlapAnalyzerClampZoneTests
         Assert.Equal(overlaps, report.ClampFindings.Any(f => f.PartBName.Contains("tiny")));
     }
 
+    // PM 407f5eb7: real material, not the 0.001 arc flattening, decides a tiny clamp.
+    [Theory]
+    [InlineData("rect", 8.00002, 0.5, true)]
+    [InlineData("rect", 8.00005, 0.5, false)]
+    [InlineData("disk", 1.9998, 0, true)]
+    [InlineData("disk", 2.0002, 0, false)]
+    public void TinyClampIsJudgedAgainstRealMaterial(string material, double a, double b, bool overlaps)
+    {
+        Program program;
+        Box zone;
+        if (material == "rect")
+        {
+            program = Rect(8.00004, 2);
+            zone = new Box(a, b, 1e-5, 1e-5);
+        }
+        else
+        {
+            program = new Program();
+            program.MoveTo(12, 10);
+            program.ArcTo(8, 10, 10, 10, RotationType.CCW);
+            program.ArcTo(12, 10, 10, 10, RotationType.CCW);
+            var cx = 10 + a * System.Math.Cos(0.02);
+            var cy = 10 + a * System.Math.Sin(0.02);
+            zone = new Box(cx - 0.000005, cy - 0.000005, 1e-5, 1e-5);
+        }
+        var parts = new List<Part> { new(new Drawing(material, program), new Vector(0, 0)) };
+
+        var report = PlateOverlapAnalyzer.Analyze(
+            PlateOverlapAnalyzer.Capture(parts, new[] { new ClampZone("tiny", zone) }));
+
+        Assert.True(report.IsComplete, string.Join("; ", report.Issues.Select(issue => issue.Message)));
+        Assert.Equal(overlaps, report.ClampFindings.Count > 0);
+    }
+
     private static string Describe(PlateOverlapReport report) =>
         string.Join(";", report.Pairs.Select(p => $"{p.PartAId}/{p.PartBId}:{p.Area:R}"))
         + "|"