diff -Nur a21glossary-0.4.11/class.tx_a21glossary.php a21glossary/class.tx_a21glossary.php
--- a21glossary-0.4.11/class.tx_a21glossary.php	2010-02-08 17:11:45.000000000 +0100
+++ a21glossary/class.tx_a21glossary.php	2010-02-08 17:09:48.000000000 +0100
@@ -108,10 +108,24 @@
 					}
 						// replace all words except the content within tags
 						/*	old version, does not work with characters >128 properly (e.g. german umlauts):				$searchArray[] = '/'.'(?!<.*?)\b'.preg_quote($row['shortcut']?$row['shortcut']:$row['short'],'/').'\b(?![^<>]*?>)'.'/us'.$caseSensitive; */
+					// Check 700 characters only to prevent an hang-up of preg_replace(), if no `<a' or `</a' is there.
+					define('PREG_MAX_CHARS', '700');
+					define('PREG_ACR_TAG', '(<acronym\s)');
+					define('PREG_ABBR_TAG', '(<abbr\s)');
+					define('PREG_A_TAG', '(<a\s)');
+					define('PREG_NOT_A_TAG', '([^<]|(<[^a])|(<a\S))');
+					define('PREG_NOT_A_END_TAG', '([^<]|(<[^\/])|(<\/[^a]))');
+					define('PREG_A_END_TAG', '(<\/a>)');
+					$tempSearch = '(?<=\s|[[:punct:]])'.$this->a21quote($row['shortcut']?$row['shortcut']:$row['short'],'/').'(?=\s|[[:punct:]])';
 					if ($generateLink) {							// if a link should be generated, then replace at this point only the words wich are already wrapped in a link (we make no nested links!)
-						$searchArray[] = '/'.'(?!<a.*?)(?!<.*?)(?<=\s|[[:punct:]])'.$this->a21quote($row['shortcut']?$row['shortcut']:$row['short'],'/').'(?=\s|[[:punct:]])(?![^<>]*?>)(?=.*<\/a>)'.'/'.$caseSensitive.$PCREmodifiersLink;
+						$searchArray[] = '/'.$tempSearch
+						  .'(?=[^>]*?<)' // Is inside an HTML tag?
+						  .'(?='.PREG_NOT_A_TAG.'{0,'.PREG_MAX_CHARS.'}?' // Is an `<a ' between shortcut and ...
+						    .PREG_A_END_TAG.')'.'/'.$caseSensitive.$PCREmodifiersLink; // `</a>'? Means that it is nested between `<a>shortcut</a>'
 					} else {											// normal procedure: all words not within of tags, wich are divided by whitespace or punctuation signs will be replaced
-						$searchArray[] = '/'.'(?!<.*?)(?<=\s|[[:punct:]])'.$this->a21quote($row['shortcut']?$row['shortcut']:$row['short'],'/').'(?=\s|[[:punct:]])(?![^<>]*?>)'.'/'.$caseSensitive.$PCREmodifiers;
+						$searchArray[] = '/'.$tempSearch
+						  .'(?=[^>]*?<|$)' // Is inside an HTML tag?
+						  .'/'.$caseSensitive.$PCREmodifiersLink;
 					}
 						// if the page language is identical with the language of the glossary word or is not defined at all, then the lang attribute will not be shown
 						// if the language of the word is defined and different to the current page language, then the lang attribute is added
@@ -138,8 +152,14 @@
 					$replaceArray[] = $result;
 						// if the record is marked to be linkable or the HTML element is configured to be linkable, then wrap the result in a link to
 					if ($generateLink) {
-							// the same condition as above, additionally the word must not be wrapped in a link (?!.*<\/a>) - otherwise we would produce nested links
-						$searchArray[] = '/'.'(?!<a.*?)(?!<.*?)(?<=\s|[[:punct:]])'.$this->a21quote($row['shortcut']?$row['shortcut']:$row['short'],'/').'(?=\s|[[:punct:]])(?![^<>]*?>)(?!.*<\/a>)/'.$caseSensitive.$PCREmodifiersLink;
+						$searchArray[] = '/'.$tempSearch
+						  .'(?=[^>]*?<)' // Is inside an HTML tag?
+						  .'(?='
+						    .'('.PREG_NOT_A_END_TAG.'{'.PREG_MAX_CHARS.'}?)' // We are using a link if there is no `<a ' or `</a>'
+						    .'|('.PREG_NOT_A_END_TAG.'{0,'.PREG_MAX_CHARS.'}?' // Is an `</a' between shortcut and ...
+						      .'('.PREG_A_TAG.'|'.PREG_ABBR_TAG.'|'.PREG_ACR_TAG.'|$))' // `<a ' | EOF? Means that it is NOT nested between `<a></a>' tags
+						  .')'.'/'.$caseSensitive.$PCREmodifiersLink;
+
 						$replaceArray[] = $cObj->typolink($result,$conf['typolink.']);
 					}
 				}