From 5f26a73ea9f0a3eb0d6f16e61904565ec547be61 Mon Sep 17 00:00:00 2001
From: Michele Bastione <michele.bastione@gmail.com>
Date: Sat, 13 Sep 2025 21:16:57 +0200
Subject: [PATCH 1/2] Fixes issue 876 on the maintenance branch

---
 .../ExcelOpenXmlSheetWriter.DefaultOpenXml.cs |  3 +++
 tests/MiniExcelTests/MiniExcelIssueTests.cs   | 20 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs b/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs
index 5f887da6..40bff72a 100644
--- a/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs
+++ b/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs
@@ -26,6 +26,9 @@ private IEnumerable<Tuple<SheetDto, object>> GetSheets()
             {
                 foreach (var sheet in dictionary)
                 {
+                    if (sheet.Key.Length > 31)
+                        throw new ArgumentException("Sheet names must be less than 31 characters");
+                    
                     sheetId++;
                     var sheetInfos = GetSheetInfos(sheet.Key);
                     yield return Tuple.Create(sheetInfos.ToDto(sheetId), sheet.Value);
diff --git a/tests/MiniExcelTests/MiniExcelIssueTests.cs b/tests/MiniExcelTests/MiniExcelIssueTests.cs
index c49c32f5..a4be971d 100644
--- a/tests/MiniExcelTests/MiniExcelIssueTests.cs
+++ b/tests/MiniExcelTests/MiniExcelIssueTests.cs
@@ -4699,4 +4699,24 @@ public void TestIssue869(string fileName, DateOnlyConversionMode mode, bool thro
             }
         }
     }
+    
+    [Fact]
+    public void TestIssue876()
+    {
+        var someTable = new[] 
+        {
+            new { Name = "Jack", Age = 25 }, 
+        };
+
+        var sheets = new Dictionary<string, object>
+        {
+            ["SomeVeryLongNameWithMoreThan31Characters"] = someTable
+        };
+
+        Assert.Throws<ArgumentException>(() =>
+        {
+            using var outputPath = AutoDeletingPath.Create();
+            MiniExcel.SaveAs(outputPath.ToString(), sheets);
+        });
+    }
 }
\ No newline at end of file

From 3c9f8af00ab4d8be8715bd5178a49664da25190d Mon Sep 17 00:00:00 2001
From: Michele Bastione <michele.bastione@gmail.com>
Date: Sat, 13 Sep 2025 21:29:39 +0200
Subject: [PATCH 2/2] Moved check for sheet name length after the GetSheetInfos
 call

Signed-off-by: Michele Bastione <michele.bastione@gmail.com>
---
 .../OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs      | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs b/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs
index 40bff72a..639c50e2 100644
--- a/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs
+++ b/src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs
@@ -26,11 +26,11 @@ private IEnumerable<Tuple<SheetDto, object>> GetSheets()
             {
                 foreach (var sheet in dictionary)
                 {
-                    if (sheet.Key.Length > 31)
-                        throw new ArgumentException("Sheet names must be less than 31 characters");
-                    
                     sheetId++;
                     var sheetInfos = GetSheetInfos(sheet.Key);
+                    if (sheetInfos.ExcelSheetName.Length > 31)
+                        throw new ArgumentException("Sheet names must be less than 31 characters");
+
                     yield return Tuple.Create(sheetInfos.ToDto(sheetId), sheet.Value);
                 }
 
@@ -427,3 +427,4 @@ private string GetCellXfId(string styleIndex)
         }
     }
 }
+