diff --git a/WebCore/ChangeLog b/WebCore/ChangeLog
index ba5bc9eb3d4e61e212eefb8f54c385be5c50e767..5687faedab229e860be5304a19bdbc37fcc4e6ba 100644
--- a/WebCore/ChangeLog
+++ b/WebCore/ChangeLog
@@ -1,3 +1,16 @@
+2009-01-23  Chris Fleizach  <cfleizach@apple.com>
+
+        Reviewed by Beth Dakin.
+
+        Bug 23509: Crash at -[WebCoreAXObject doAXNextSentenceEndTextMarkerForTextMarker:]
+        https://bugs.webkit.org/show_bug.cgi?id=23509
+  
+        Add null checking around next/previous sentence retrieval in AX code
+
+        * page/AccessibilityObject.cpp:
+        (WebCore::AccessibilityObject::nextSentenceEndPosition):
+        (WebCore::AccessibilityObject::previousSentenceStartPosition):
+
 2009-01-23  David Hyatt  <hyatt@apple.com>
 
         Fix for <rdar://problem/6518850> REGRESSION: hover feedback not showing on many sites
diff --git a/WebCore/page/AccessibilityObject.cpp b/WebCore/page/AccessibilityObject.cpp
index e868da28c84281a8ad685c7b4afdbd68ad3d1153..67b95fde1499aa8013d4126601ca3fe969162b19 100644
--- a/WebCore/page/AccessibilityObject.cpp
+++ b/WebCore/page/AccessibilityObject.cpp
@@ -739,7 +739,13 @@ VisiblePosition AccessibilityObject::nextSentenceEndPosition(const VisiblePositi
     // an empty line is considered a sentence. If it's skipped, then the sentence parser will not
     // see this empty line.  Instead, return the end position of the empty line.
     VisiblePosition endPosition;
-    String lineString = plainText(makeRange(startOfLine(visiblePos), endOfLine(visiblePos)).get());
+    VisiblePosition startOfLinePosition = startOfLine(nextVisiblePos);
+    VisiblePosition endOfLinePosition = endOfLine(nextVisiblePos);
+
+    String lineString;
+    if (startOfLinePosition.isNotNull() && endOfLinePosition.isNotNull())
+        lineString = plainText(makeRange(startOfLinePosition, endOfLinePosition).get());
+
     if (lineString.isEmpty())
         endPosition = nextVisiblePos;
     else
@@ -762,7 +768,13 @@ VisiblePosition AccessibilityObject::previousSentenceStartPosition(const Visible
 
     // treat empty line as a separate sentence.
     VisiblePosition startPosition;
-    String lineString = plainText(makeRange(startOfLine(previousVisiblePos), endOfLine(previousVisiblePos)).get());
+    VisiblePosition startOfLinePosition = startOfLine(previousVisiblePos);
+    VisiblePosition endOfLinePosition = endOfLine(previousVisiblePos);
+    
+    String lineString;
+    if (startOfLinePosition.isNotNull() && endOfLinePosition.isNotNull())
+        lineString = plainText(makeRange(startOfLinePosition, endOfLinePosition).get());
+    
     if (lineString.isEmpty())
         startPosition = previousVisiblePos;
     else