diff --git a/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php b/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php
index 25a841fd4a..6ddbb67223 100644
--- a/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php
+++ b/src/applications/repository/worker/commitchangeparser/git/PhabricatorRepositoryGitCommitChangeParserWorker.php
@@ -30,13 +30,39 @@ final class PhabricatorRepositoryGitCommitChangeParserWorker
       return;
     }
 
-    // NOTE: "--pretty=format: " is to disable log output, we only want the
-    // part we get from "--raw".
-    list($raw) = $repository->execxLocalCommand(
-      'log -n1 -M -C -B --find-copies-harder --raw -t '.
-        '--abbrev=40 --pretty=format: %s',
+    // Check if the commit has parents. We're testing to see whether it is the
+    // first commit in history (in which case we must use "git log") or some
+    // other commit (in which case we can use "git diff"). We'd rather use
+    // "git diff" because it has the right behavior for merge commits, but
+    // it requires the commit to have a parent that we can diff against. The
+    // first commit doesn't, so "commit^" is not a valid ref.
+    list($parents) = $repository->execxLocalCommand(
+      'log -n1 --format=%s %s',
+      '%P',
       $commit->getCommitIdentifier());
 
+    $use_log = !strlen(trim($parents));
+    if ($use_log) {
+      // This is the first commit so we need to use "log". We know it's not a
+      // merge commit because it couldn't be merging anything, so this is safe.
+
+      // NOTE: "--pretty=format: " is to disable diff output, we only want the
+      // part we get from "--raw".
+      list($raw) = $repository->execxLocalCommand(
+        'log -n1 -M -C -B --find-copies-harder --raw -t '.
+          '--pretty=format: --abbrev=40 %s',
+        $commit->getCommitIdentifier());
+    } else {
+      // Otherwise, we can use "diff", which will give us output for merges.
+      // We diff against the first parent, as this is generally the expectation
+      // and results in sensible behavior.
+      list($raw) = $repository->execxLocalCommand(
+        'diff -n1 -M -C -B --find-copies-harder --raw -t '.
+          '--abbrev=40 %s^1 %s',
+        $commit->getCommitIdentifier(),
+        $commit->getCommitIdentifier());
+    }
+
     $changes = array();
     $move_away = array();
     $copy_away = array();