diff --git a/Classes/PHPExcel/Calculation/TextData.php b/Classes/PHPExcel/Calculation/TextData.php
index aceafc6..3c3ed22 100644
--- a/Classes/PHPExcel/Calculation/TextData.php
+++ b/Classes/PHPExcel/Calculation/TextData.php
@@ -239,9 +239,12 @@ class PHPExcel_Calculation_TextData {
 				$haystack = ($haystack) ? PHPExcel_Calculation::getTRUE() : PHPExcel_Calculation::getFALSE();
 			}
 
-			if (($offset > 0) && (strlen($haystack) > $offset)) {
+			if (($offset > 0) && (PHPExcel_Shared_String::CountCharacters($haystack) > $offset)) {
+				if (PHPExcel_Shared_String::CountCharacters($needle) == 0) {
+					return $offset;
+				}
 				if (function_exists('mb_strpos')) {
-					$pos = mb_strpos($haystack, $needle, --$offset,'UTF-8');
+					$pos = mb_strpos($haystack, $needle, --$offset, 'UTF-8');
 				} else {
 					$pos = strpos($haystack, $needle, --$offset);
 				}
@@ -272,7 +275,10 @@ class PHPExcel_Calculation_TextData {
 				$haystack = ($haystack) ? PHPExcel_Calculation::getTRUE() : PHPExcel_Calculation::getFALSE();
 			}
 
-			if (($offset > 0) && (strlen($haystack) > $offset)) {
+			if (($offset > 0) && (PHPExcel_Shared_String::CountCharacters($haystack) > $offset)) {
+				if (PHPExcel_Shared_String::CountCharacters($needle) == 0) {
+					return $offset;
+				}
 				if (function_exists('mb_stripos')) {
 					$pos = mb_stripos($haystack, $needle, --$offset,'UTF-8');
 				} else {
diff --git a/changelog.txt b/changelog.txt
index 6d0c51b..c8ab361 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -92,7 +92,7 @@ Fixed in develop branch:
 - Bugfix:   (MBaker)     Various fixes to Chart handling
 - Bugfix:   (MBaker)     Work item 18370 - Error loading xlsx file with column breaks
 - Bugfix:   (MBaker)     OOCalc Reader now handles percentage and currency data types
-- Bugfix:   (MBaker)     OOCalc Reader modified to process number-rows-repeated
+- Bugfix:   (MBaker)     Work Item 18415- mb_stripos empty delimiter
 
 
 2012-05-19 (v1.7.7):
diff --git a/unitTests/rawTestData/Calculation/TextData/FIND.data b/unitTests/rawTestData/Calculation/TextData/FIND.data
index 677d4f0..411150d 100644
--- a/unitTests/rawTestData/Calculation/TextData/FIND.data
+++ b/unitTests/rawTestData/Calculation/TextData/FIND.data
@@ -9,3 +9,5 @@
 "k",	"Mark Baker",	5,	8
 "a",	"Mark Baker",	3,	7
 "BITE",	"BIT",			"#VALUE!"
+"",	"Mark Baker",		1
+"",	"Mark Baker",	8,	8