diff --git a/OpenNest.WinForms.Tests/Forms/BomImportFormTests.cs b/OpenNest.WinForms.Tests/Forms/BomImportFormTests.cs
index 6357dc7..9274ee0 100644
--- a/OpenNest.WinForms.Tests/Forms/BomImportFormTests.cs
+++ b/OpenNest.WinForms.Tests/Forms/BomImportFormTests.cs
@@ -76,6 +76,30 @@ public class BomImportFormTests
         });
     }
 
+    [Theory]
+    [InlineData("colQty", "0")]
+    [InlineData("colQty", "abc")]
+    [InlineData("colThickness", "-1")]
+    [InlineData("colThickness", "abc")]
+    public void ProgrammaticCommitOfInvalidText_KeepsTheRowsValue(string column, string text)
+    {
+        RunSta(() =>
+        {
+            using var form = Show(out var parts);
+            var part = Ready("PT01", qty: 2);
+            form.LoadRows(new[] { part });
+
+            parts.CurrentCell = parts.Rows[0].Cells[column];
+            Assert.True(parts.BeginEdit(selectAll: true));
+            parts.EditingControl!.Text = text;
+            Assert.True(parts.EndEdit());
+
+            Assert.Equal(2, part.Qty);
+            Assert.Equal(0.25, part.Thickness);
+            Assert.Equal(BomRowStatus.Ready, part.Status);
+        });
+    }
+
     [Fact]
     public void Edits_ChangeThePartShownInThatRow_AfterTheRowsAreReloadedInAnotherOrder()
     {
@@ -131,7 +155,7 @@ public class BomImportFormTests
             form.LoadRows(new[] { first, second });
 
             Assert.True(Edit(parts, 0, "colMaterial", " "));
-            Assert.Null(first.Material);
+            Assert.Equal("", first.Material);
             Assert.Equal("Needs material", parts.Rows[0].Cells["colStatus"].Value);
 
             Assert.False(Edit(parts, 1, "colThickness", "abc"));
@@ -156,12 +180,22 @@ public class BomImportFormTests
         return form;
     }
 
+    /// <summary>
+    /// Types <paramref name="text"/> into the cell and presses Enter, which
+    /// validates the cell the way the operator's commit does. Returns true
+    /// when the edit was accepted (the cell left edit mode).
+    /// </summary>
     private static bool Edit(DataGridView grid, int row, string column, string text)
     {
         grid.CurrentCell = grid.Rows[row].Cells[column];
         Assert.True(grid.BeginEdit(selectAll: true));
         grid.EditingControl!.Text = text;
-        return grid.EndEdit();
+        var processEnterKey = typeof(DataGridView).GetMethod(
+            "ProcessEnterKey",
+            BindingFlags.Instance | BindingFlags.NonPublic
+        )!;
+        processEnterKey.Invoke(grid, new object[] { Keys.Enter });
+        return !grid.IsCurrentCellInEditMode;
     }
 
     private static DataTable GroupsTable(BomImportForm form) =>
diff --git a/OpenNest/Forms/BomImportForm.Designer.cs b/OpenNest/Forms/BomImportForm.Designer.cs
index 37fb528..b847ea1 100644
--- a/OpenNest/Forms/BomImportForm.Designer.cs
+++ b/OpenNest/Forms/BomImportForm.Designer.cs
@@ -326,6 +326,7 @@ namespace OpenNest.Forms
             // colThickness
             //
             thicknessCellStyle.Alignment = System.Windows.Forms.DataGridViewContentAlignment.MiddleRight;
+            thicknessCellStyle.DataSourceNullValue = null;
             thicknessCellStyle.Format = "0.####";
             colThickness.DataPropertyName = "Thickness";
             colThickness.DefaultCellStyle = thicknessCellStyle;
@@ -337,6 +338,7 @@ namespace OpenNest.Forms
             // colQty
             //
             qtyCellStyle.Alignment = System.Windows.Forms.DataGridViewContentAlignment.MiddleRight;
+            qtyCellStyle.DataSourceNullValue = null;
             colQty.DataPropertyName = "Qty";
             colQty.DefaultCellStyle = qtyCellStyle;
             colQty.FillWeight = 50F;
diff --git a/OpenNest/Forms/BomImportForm.cs b/OpenNest/Forms/BomImportForm.cs
index 88e7cd7..2d4077f 100644
--- a/OpenNest/Forms/BomImportForm.cs
+++ b/OpenNest/Forms/BomImportForm.cs
@@ -181,7 +181,7 @@ namespace OpenNest.Forms
                 error = "Enter a whole number of 1 or more.";
             else if (
                 e.ColumnIndex == colThickness.Index
-                && !string.IsNullOrWhiteSpace(text)
+                && !string.IsNullOrEmpty(text)
                 && !TryParseThickness(text, out _)
             )
                 error = "Enter a thickness greater than 0, or leave it blank.";
@@ -191,27 +191,42 @@ namespace OpenNest.Forms
                 e.Cancel = true;
         }
 
+        // CellValidating refuses bad text when the operator commits a cell. A
+        // programmatic EndEdit() skips validation, so parsing keeps the row's
+        // current value rather than storing text validation would refuse. The
+        // grid ignores a null parsed value, so a blank thickness is left to the
+        // column's DataSourceNullValue (null).
         private void DgvParts_CellParsing(object sender, DataGridViewCellParsingEventArgs e)
         {
-            var text = e.Value?.ToString();
+            var text = e.Value?.ToString() ?? "";
+            var part = PartAt(e.RowIndex);
 
-            if (e.ColumnIndex == colQty.Index && BomQuantity.TryParse(text, out var qty))
+            if (e.ColumnIndex == colQty.Index)
             {
-                e.Value = qty;
-                e.ParsingApplied = true;
+                if (BomQuantity.TryParse(text, out var qty))
+                    Parsed(e, qty);
+                else if (part?.Qty is int current)
+                    Parsed(e, current);
             }
-            else if (e.ColumnIndex == colThickness.Index)
+            else if (e.ColumnIndex == colThickness.Index && text.Length > 0)
             {
-                e.Value = TryParseThickness(text, out var thickness) ? thickness : null;
-                e.ParsingApplied = true;
+                if (TryParseThickness(text, out var thickness))
+                    Parsed(e, thickness);
+                else if (part?.Thickness is double current)
+                    Parsed(e, current);
             }
             else if (e.ColumnIndex == colMaterial.Index)
             {
-                e.Value = string.IsNullOrWhiteSpace(text) ? null : text;
-                e.ParsingApplied = true;
+                Parsed(e, text.Trim());
             }
         }
 
+        private static void Parsed(DataGridViewCellParsingEventArgs e, object value)
+        {
+            e.Value = value;
+            e.ParsingApplied = true;
+        }
+
         private void DgvParts_CellEndEdit(object sender, DataGridViewCellEventArgs e)
         {
             dgvParts.Rows[e.RowIndex].Cells[e.ColumnIndex].ErrorText = "";