diff --git a/src/utils/PhutilProseDifferenceEngine.php b/src/utils/PhutilProseDifferenceEngine.php
--- a/src/utils/PhutilProseDifferenceEngine.php
+++ b/src/utils/PhutilProseDifferenceEngine.php
@@ -3,21 +3,10 @@
 final class PhutilProseDifferenceEngine extends Phobject {
 
   public function getDiff($u, $v) {
-    $diff = id(new PhutilProseDiff());
-
-    $this->buildDiff($diff, $u, $v, 1);
-    $diff->reorderParts();
-
-    return $diff;
+    return $this->buildDiff($u, $v, 1);
   }
 
-  private function buildDiff(PhutilProseDiff $diff, $u, $v, $level) {
-    if ($level == 4) {
-      $diff->addPart('-', $u);
-      $diff->addPart('+', $v);
-      return;
-    }
-
+  private function buildDiff($u, $v, $level) {
     $u_parts = $this->splitCorpus($u, $level);
     $v_parts = $this->splitCorpus($v, $level);
 
@@ -38,6 +27,7 @@
     $edits = $matrix->getEditString();
     $edits_length = strlen($edits);
 
+    $diff = new PhutilProseDiff();
     for ($ii = 0; $ii < $edits_length; $ii++) {
       $c = $edits[$ii];
       if ($c == 's') {
@@ -51,7 +41,8 @@
         $diff->addPart('+', $v_parts[$v_pos]);
         $v_pos++;
       } else if ($c == 'x') {
-        $this->buildDiff($diff, $u_parts[$u_pos], $v_parts[$v_pos], $level + 1);
+        $diff->addPart('-', $u_parts[$u_pos]);
+        $diff->addPart('+', $v_parts[$v_pos]);
         $u_pos++;
         $v_pos++;
       } else {
@@ -61,6 +52,88 @@
             $c));
       }
     }
+
+    $diff->reorderParts();
+
+    // If we just built a character-level diff, we're all done and do not
+    // need to go any deeper.
+    if ($level == 3) {
+      return $diff;
+    }
+
+    $blocks = array();
+    $block = null;
+    foreach ($diff->getParts() as $part) {
+      $type = $part['type'];
+      $text = $part['text'];
+      switch ($type) {
+        case '=':
+          if ($block) {
+            $blocks[] = $block;
+            $block = null;
+          }
+          $blocks[] = array(
+            'type' => $type,
+            'text' => $text,
+          );
+          break;
+        case '-':
+          if (!$block) {
+            $block = array(
+              'type' => '!',
+              'old' => '',
+              'new' => '',
+            );
+          }
+          $block['old'] .= $text;
+          break;
+        case '+':
+          if (!$block) {
+            $block = array(
+              'type' => '!',
+              'old' => '',
+              'new' => '',
+            );
+          }
+          $block['new'] .= $text;
+          break;
+      }
+    }
+
+    if ($block) {
+      $blocks[] = $block;
+    }
+
+    $result = new PhutilProseDiff();
+    foreach ($blocks as $block) {
+      $type = $block['type'];
+      if ($type == '=') {
+        $result->addPart('=', $block['text']);
+      } else {
+        $old = $block['old'];
+        $new = $block['new'];
+        if (!strlen($old) && !strlen($new)) {
+          // Nothing to do.
+        } else if (!strlen($old)) {
+          $result->addPart('+', $new);
+        } else if (!strlen($new)) {
+          $result->addPart('-', $old);
+        } else {
+          $subdiff = $this->buildDiff(
+            $old,
+            $new,
+            $level + 1);
+
+          foreach ($subdiff->getParts() as $part) {
+            $result->addPart($part['type'], $part['text']);
+          }
+        }
+      }
+    }
+
+    $result->reorderParts();
+
+    return $result;
   }
 
   private function splitCorpus($corpus, $level) {
diff --git a/src/utils/__tests__/PhutilProseDiffTestCase.php b/src/utils/__tests__/PhutilProseDiffTestCase.php
--- a/src/utils/__tests__/PhutilProseDiffTestCase.php
+++ b/src/utils/__tests__/PhutilProseDiffTestCase.php
@@ -130,6 +130,28 @@
         "+ \n\n- ccc ccc ccc",
       ),
       pht('Diff with new trailing content.'));
+
+    $this->assertProseParts(
+      'aaa aaa aaa aaa, bbb bbb bbb bbb.',
+      'aaa aaa aaa aaa bbb bbb bbb bbb.',
+      array(
+        '= aaa aaa aaa aaa',
+        '- ,',
+        '=  bbb bbb bbb bbb.',
+      ),
+      pht('Diff with a removed comma.'));
+
+    $this->assertProseParts(
+      'aaa aaa aaa aaa, bbb bbb bbb bbb.',
+      "aaa aaa aaa aaa bbb bbb bbb bbb.\n\n- ccc ccc ccc!",
+      array(
+        '= aaa aaa aaa aaa',
+        '- ,',
+        '=  bbb bbb bbb bbb.',
+        "+ \n\n- ccc ccc ccc!",
+      ),
+      pht('Diff with a removed comma and new trailing content.'));
+
   }
 
   private function assertProseParts($old, $new, array $expect_parts, $label) {