diff --git a/src/infrastructure/diff/prose/PhutilProseDifferenceEngine.php b/src/infrastructure/diff/prose/PhutilProseDifferenceEngine.php
--- a/src/infrastructure/diff/prose/PhutilProseDifferenceEngine.php
+++ b/src/infrastructure/diff/prose/PhutilProseDifferenceEngine.php
@@ -148,7 +148,7 @@
         // whitespace at the end.
 
         $matches = null;
-        preg_match('/^(\s*)(.*?)(\s*)\z/', $result, $matches);
+        preg_match('/^(\s*)(.*?)(\s*)\z/s', $result, $matches);
 
         if (strlen($matches[1])) {
           $results[] = $matches[1];
diff --git a/src/infrastructure/diff/prose/__tests__/PhutilProseDiffTestCase.php b/src/infrastructure/diff/prose/__tests__/PhutilProseDiffTestCase.php
--- a/src/infrastructure/diff/prose/__tests__/PhutilProseDiffTestCase.php
+++ b/src/infrastructure/diff/prose/__tests__/PhutilProseDiffTestCase.php
@@ -30,6 +30,14 @@
       ),
       pht('Remove Paragraph'));
 
+    $this->assertProseParts(
+       'xxx',
+       "xxxyyy\n.zzz",
+       array(
+         '= xxx',
+         "+ yyy\n.zzz",
+       ),
+       pht('Amend paragraph, and add paragraph starting with punctuation'));
 
     // Without smoothing, the alogorithm identifies that "shark" and "cat"
     // both contain the letter "a" and tries to express this as a very