--- src/java/org/apache/poi/hssf/model/LinkTable.java	(revision 1815000)
+++ src/java/org/apache/poi/hssf/model/LinkTable.java	(working copy)
@@ -459,7 +459,7 @@ 
 
     private static int getSheetIndex(String[] sheetNames, String sheetName) {
         for (int i = 0; i < sheetNames.length; i++) {
-            if (sheetNames[i].equals(sheetName)) {
+            if (sheetNames[i].equalsIgnoreCase(sheetName)) {
                 return i;
             }
 
--- src/java/org/apache/poi/ss/formula/ptg/ExternSheetNameResolver.java	(revision 1815000)
+++ src/java/org/apache/poi/ss/formula/ptg/ExternSheetNameResolver.java	(working copy)
@@ -45,7 +45,7 @@ 
             }
             if (externalSheet instanceof ExternalSheetRange) {
                 ExternalSheetRange r = (ExternalSheetRange)externalSheet;
-                if (! r.getFirstSheetName().equals(r.getLastSheetName())) {
+                if (! r.getFirstSheetName().equalsIgnoreCase(r.getLastSheetName())) {
                     sb.append(':');
                     SheetNameFormatter.appendFormat(sb, r.getLastSheetName());
                 }
@@ -59,7 +59,7 @@ 
                 sb.append("#REF"); // note - '!' added just once below
             } else {
                 SheetNameFormatter.appendFormat(sb, firstSheetName);
-                if (! firstSheetName.equals(lastSheetName)) {
+                if (! firstSheetName.equalsIgnoreCase(lastSheetName)) {
                     sb.append(':');
                     sb.append(lastSheetName);
                 }
--- src/java/org/apache/poi/ss/util/CellReference.java	(revision 1815000)
+++ src/java/org/apache/poi/ss/util/CellReference.java	(working copy)
@@ -560,7 +560,7 @@ 
                 && _isColAbs == cr._isColAbs
                 && ((_sheetName == null)
                         ? (cr._sheetName == null)
-                        : _sheetName.equals(cr._sheetName));
+                        : _sheetName.equalsIgnoreCase(cr._sheetName));
     }
 
     @Override
@@ -570,7 +570,7 @@ 
         result = 31 * result + _colIndex;
         result = 31 * result + (_isRowAbs ? 1 : 0);
         result = 31 * result + (_isColAbs ? 1 : 0);
-        result = 31 * result + (_sheetName == null ? 0 : _sheetName.hashCode());
+        result = 31 * result + (_sheetName == null ? 0 : _sheetName.toLowerCase(Locale.ROOT).hashCode());
         return result;
     }
 }
--- src/ooxml/java/org/apache/poi/xssf/usermodel/BaseXSSFEvaluationWorkbook.java	(revision 1815000)
+++ src/ooxml/java/org/apache/poi/xssf/usermodel/BaseXSSFEvaluationWorkbook.java	(working copy)
@@ -308,7 +308,7 @@ 
             workbookName = null;
         }
         
-        if (lastSheetName == null || firstSheetName.equals(lastSheetName)) {
+        if (lastSheetName == null || firstSheetName.equalsIgnoreCase(lastSheetName)) {
             return new ExternalSheet(workbookName, firstSheetName);
         } else {
             return new ExternalSheetRange(workbookName, firstSheetName, lastSheetName);
--- src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java	(revision 1815000)
+++ src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java	(working copy)
@@ -857,7 +857,7 @@ 
             String sheetName = XSSFRelation.WORKSHEET.getFileName(sheetNumber);
             for(POIXMLDocumentPart relation : getRelations()) {
                 if(relation.getPackagePart() != null && 
-                        sheetName.equals(relation.getPackagePart().getPartName().getName())) {
+                        sheetName.equalsIgnoreCase(relation.getPackagePart().getPartName().getName())) {
                     // name is taken => try next one
                     sheetNumber++;
                     continue outerloop;
@@ -1595,7 +1595,7 @@ 
         WorkbookUtil.validateSheetName(sheetname);
 
         // Do nothing if no change
-        if (sheetname.equals(oldSheetName)) {
+        if (sheetname.equalsIgnoreCase(oldSheetName)) {
             return;
         }