diff --git a/src/parser/ArcanistDiffParser.php b/src/parser/ArcanistDiffParser.php
--- a/src/parser/ArcanistDiffParser.php
+++ b/src/parser/ArcanistDiffParser.php
@@ -288,9 +288,11 @@
 
       if (isset($match['type'])) {
         if ($match['type'] == 'diff --git') {
-          list($old, $new) = self::splitGitDiffPaths($match['oldnew']);
-          $match['old'] = $old;
-          $match['cur'] = $new;
+          $filename = self::splitGitDiffPaths($match['oldnew']);
+          if (isset($filename)) {
+            $match['old'] = $filename;
+            $match['cur'] = $filename;
+          }
         }
       }
 
@@ -1308,46 +1310,6 @@
 
 
   /**
-   * Strip prefixes off paths from `git diff`. By default git uses a/ and b/,
-   * but you can set `diff.mnemonicprefix` to get a different set of prefixes,
-   * or use `--no-prefix`, `--src-prefix` or `--dst-prefix` to set these to
-   * other arbitrary values.
-   *
-   * We strip the default and mnemonic prefixes, and trust the user knows what
-   * they're doing in the other cases.
-   *
-   * @param   string Path to strip.
-   * @return  string Stripped path.
-   */
-  public static function stripGitPathPrefix($path) {
-
-    static $regex;
-    if ($regex === null) {
-      $prefixes = array(
-        // These are the defaults.
-        'a/',
-        'b/',
-
-        // These show up when you set "diff.mnemonicprefix".
-        'i/',
-        'c/',
-        'w/',
-        'o/',
-        '1/',
-        '2/',
-      );
-
-      foreach ($prefixes as $key => $prefix) {
-        $prefixes[$key] = preg_quote($prefix, '@');
-      }
-      $regex = '@^('.implode('|', $prefixes).')@S';
-    }
-
-    return preg_replace($regex, '', $path);
-  }
-
-
-  /**
    * Split the paths on a "diff --git" line into old and new paths. This
    * is difficult because they may be ambiguous if the files contain spaces.
    *
@@ -1358,49 +1320,36 @@
     $matches = null;
     $paths = rtrim($paths, "\r\n");
 
-    $patterns = array(
-      // Try quoted paths, used for unicode filenames or filenames with quotes.
-      '@^(?P<old>"(?:\\\\.|[^"\\\\]+)+") (?P<new>"(?:\\\\.|[^"\\\\]+)+")$@',
-
-      // Try paths without spaces.
-      '@^(?P<old>[^ ]+) (?P<new>[^ ]+)$@',
-
-      // Try paths with well-known prefixes.
-      '@^(?P<old>[abicwo12]/.*) (?P<new>[abicwo12]/.*)$@',
-
-      // Try the exact same string twice in a row separated by a space.
-      // This can hit a false positive for moves from files like "old file old"
-      // to "file", but such a case combined with custom diff prefixes is
-      // incredibly obscure.
-      '@^(?P<old>.*) (?P<new>\\1)$@',
-    );
-
-    foreach ($patterns as $pattern) {
-      if (preg_match($pattern, $paths, $matches)) {
-        break;
-      }
-    }
-
-    if (!$matches) {
-      throw new Exception(
-        pht(
-          "Input diff contains ambiguous line '%s'. This line is ambiguous ".
-          "because there are spaces in the file names, so the parser can not ".
-          "determine where the file names begin and end. To resolve this ".
-          "ambiguity, use standard prefixes ('a/' and 'b/') when ".
-          "generating diffs.",
-          "diff --git {$paths}"));
+    // Try the exact same string twice in a row separated by a
+    // space, with an optional prefix.  This can hit a false
+    // positive for moves from files like "old file old" to "file",
+    // but such a cases will be caught by the "rename from" /
+    // "rename to" lines.
+    $prefix = '(?:[^/]+/)?';
+    $pattern =
+             "@^(?P<old>(?P<oldq>\"?)$prefix(?P<common>.+)\\k<oldq>)"
+             ." "
+             ."(?P<new>(?P<newq>\"?)$prefix\\k<common>\\k<newq>)$@";
+
+    if (!preg_match($pattern, $paths, $matches)) {
+      // A rename or some form; return null for now, and let the
+      // "rename from" / "rename to" lines fix it up.
+      return null;
     }
 
-    $old = $matches['old'];
-    $old = self::unescapeFilename($old);
-    $old = self::stripGitPathPrefix($old);
+    // Use the common subpart.  There may be ambiguity here: "src/file
+    // dst/file" may _either_ be a prefix-less move, or a change with
+    // two custom prefixes.  We assume it is the latter; if it is a
+    // rename, diff parsing will update based on the "rename from" /
+    // "rename to" lines.
 
-    $new = $matches['new'];
+    // This re-assembles with the differing prefixes removed, but the
+    // quoting from the original.  Necessary so we know if we should
+    // unescape characters from the common string.
+    $new = $matches['newq'].$matches['common'].$matches['newq'];
     $new = self::unescapeFilename($new);
-    $new = self::stripGitPathPrefix($new);
 
-    return array($old, $new);
+    return $new;
   }
 
 
diff --git a/src/parser/__tests__/ArcanistDiffParserTestCase.php b/src/parser/__tests__/ArcanistDiffParserTestCase.php
--- a/src/parser/__tests__/ArcanistDiffParserTestCase.php
+++ b/src/parser/__tests__/ArcanistDiffParserTestCase.php
@@ -535,7 +535,14 @@
         $this->assertEqual(1, count($changes));
         $change = head($changes);
         $this->assertEqual(
-          'dst/file',
+          'file',
+          $change->getCurrentPath());
+        break;
+      case 'custom-prefixes-edit.gitdiff':
+        $this->assertEqual(1, count($changes));
+        $change = head($changes);
+        $this->assertEqual(
+          'file',
           $change->getCurrentPath());
         break;
       case 'more-newlines.svndiff':
@@ -607,55 +614,36 @@
     }
   }
 
-  public function testGitPrefixStripping() {
-    static $tests = array(
-      'a/file.c'    => 'file.c',
-      'b/file.c'    => 'file.c',
-      'i/file.c'    => 'file.c',
-      'c/file.c'    => 'file.c',
-      'w/file.c'    => 'file.c',
-      'o/file.c'    => 'file.c',
-      '1/file.c'    => 'file.c',
-      '2/file.c'    => 'file.c',
-      'src/file.c'  => 'src/file.c',
-      'file.c'      => 'file.c',
-    );
-
-    foreach ($tests as $input => $expect) {
-      $this->assertEqual(
-        $expect,
-        ArcanistDiffParser::stripGitPathPrefix($input),
-        pht("Strip git prefix from '%s'.", $input));
-    }
-  }
-
   public function testGitPathSplitting() {
     static $tests = array(
-      'a/old.c b/new.c'       => array('old.c', 'new.c'),
-      "a/old.c b/new.c\n"     => array('old.c', 'new.c'),
-      "a/old.c b/new.c\r\n"   => array('old.c', 'new.c'),
-      'old.c new.c'           => array('old.c', 'new.c'),
-      '1/old.c 2/new.c'       => array('old.c', 'new.c'),
-      '"a/\\"quotes1\\"" "b/\\"quotes2\\""' => array(
-        '"quotes1"',
-        '"quotes2"',
-      ),
-      '"a/\\"quotes and spaces1\\"" "b/\\"quotes and spaces2\\""' => array(
-        '"quotes and spaces1"',
-        '"quotes and spaces2"',
-      ),
-      '"a/\\342\\230\\2031" "b/\\342\\230\\2032"' => array(
-        "\xE2\x98\x831",
-        "\xE2\x98\x832",
-      ),
-      'a/Core Data/old.c b/Core Data/new.c' => array(
-        'Core Data/old.c',
-        'Core Data/new.c',
-      ),
-      'some file with spaces.c some file with spaces.c' => array(
-        'some file with spaces.c',
-        'some file with spaces.c',
-      ),
+      'a/filename.c b/filename.c'         => 'filename.c',
+      "a/filename.c b/filename.c\n"       => 'filename.c',
+      "a/filename.c b/filename.c\r\n"     => 'filename.c',
+      'filename.c filename.c'             => 'filename.c',
+      '1/filename.c 2/filename.c'         => 'filename.c',
+      '"a/\\"quotes\\"" "b/\\"quotes\\""' => '"quotes"',
+      '"a/\\"quotes and spaces\\"" "b/\\"quotes and spaces\\""' =>
+        '"quotes and spaces"',
+      '"a/\\342\\230\\203" "b/\\342\\230\\203"' =>
+         "\xE2\x98\x83",
+      'a/Core Data/filename.c b/Core Data/filename.c' =>
+         'Core Data/filename.c',
+      'some file with spaces.c some file with spaces.c' =>
+         'some file with spaces.c',
+      '"foo bar.c" foo bar.c'        => 'foo bar.c',
+      '"a/foo bar.c" b/foo bar.c'    => 'foo bar.c',
+      'src/file dst/file'            => 'file',
+
+      // Renames are handled by the "rename from ..." lines later in
+      // the diff, for simplicity of parsing; thisi s also how git
+      // itself handles it.
+      'a/foo.c b/bar.c'              => null,
+      'a/foo bar.c b/baz troz.c'     => null,
+      '"a/foo bar.c" b/baz troz.c'   => null,
+      'a/foo bar.c "b/baz troz.c"'   => null,
+      '"a/foo bar.c" "b/baz troz.c"' => null,
+      'filename file with spaces.c filename file with spaces.c' =>
+        'filename file with spaces.c',
     );
 
     foreach ($tests as $input => $expect) {
@@ -665,23 +653,70 @@
         $result,
         pht('Split: %s', $input));
     }
+  }
 
 
-    static $ambiguous = array(
-      'old file with spaces.c new file with spaces.c',
-    );
-
-    foreach ($ambiguous as $input) {
-      $caught = null;
-      try {
-        ArcanistDiffParser::splitGitDiffPaths($input);
-      } catch (Exception $ex) {
-        $caught = $ex;
-      }
-      $this->assertTrue(
-        ($caught instanceof Exception),
-        pht('Ambiguous: %s', $input));
-    }
+  public function runSingleRename($diffline, $from, $to, $old, $new) {
+    $str = "diff --git $diffline\nsimilarity index 95%\n"
+         ."rename from $from\nrename to $to\n";
+    $parser = new ArcanistDiffParser();
+    $changes = $parser->parseDiff($str);
+    $this->assertTrue($changes !== null, "Parsed:\n$str");
+    $this->assertEqual(
+      $old == $new ? 1 : 2, count($changes),
+      "Parsed one change:\n$str");
+    $change = reset($changes);
+    $this->assertEqual(
+      array($old, $new),
+      array($change->getOldPath(), $change->getCurrentPath()),
+      "Successfully split: $diffline");
   }
 
+  public function testGitRenames() {
+    $this->runSingleRename('a/old.c b/new.c',
+                           'old.c',                   'new.c',
+                           'old.c',                   'new.c');
+    $this->runSingleRename('old.c new.c',
+                           'old.c',                   'new.c',
+                           'old.c',                   'new.c');
+    $this->runSingleRename('1/old.c 2/new.c',
+                           'old.c',                   'new.c',
+                           'old.c',                   'new.c');
+    $this->runSingleRename('from/file.c to/file.c',
+                           'from/file.c',             'to/file.c',
+                           'from/file.c',             'to/file.c');
+    $this->runSingleRename('"a/\\"quotes1\\"" "b/\\"quotes2\\""',
+                           '"\\"quotes1\\""',         '"\\"quotes2\\""',
+                           '"quotes1"',               '"quotes2"');
+    $this->runSingleRename('"a/\\"quotes spaces1\\"" "b/\\"quotes spaces2\\""',
+                           '"\\"quotes spaces1\\""',  '"\\"quotes spaces2\\""',
+                           '"quotes spaces1"',        '"quotes spaces2"');
+    $this->runSingleRename('"a/\\342\\230\\2031" "b/\\342\\230\\2032"',
+                           '"\\342\\230\\2031"',      '"\\342\\230\\2032"',
+                           "\xE2\x98\x831",           "\xE2\x98\x832");
+    $this->runSingleRename('a/Core Data/old.c b/Core Data/new.c',
+                           'Core Data/old.c',         'Core Data/new.c',
+                           'Core Data/old.c',         'Core Data/new.c');
+    $this->runSingleRename('file with spaces.c file with spaces.c',
+                           'file with spaces.c', 'file with spaces.c',
+                           'file with spaces.c', 'file with spaces.c');
+    $this->runSingleRename('a/non-quoted filename.c "b/quoted filename.c"',
+                           'non-quoted filename.c',   '"quoted filename.c"',
+                           'non-quoted filename.c',   'quoted filename.c');
+    $this->runSingleRename('non-quoted filename.c "quoted filename.c"',
+                           'non-quoted filename.c',   '"quoted filename.c"',
+                           'non-quoted filename.c',   'quoted filename.c');
+    $this->runSingleRename('"a/quoted filename.c" b/non quoted filename.c',
+                           '"quoted filename.c"',     'non quoted filename.c',
+                           'quoted filename.c',       'non quoted filename.c');
+    $this->runSingleRename('"quoted filename.c" non-quoted filename.c',
+                           '"quoted filename.c"',     'non-quoted filename.c',
+                           'quoted filename.c',       'non-quoted filename.c');
+    $this->runSingleRename('old file with spaces.c new file with spaces.c',
+                           'old file with spaces.c',  'new file with spaces.c',
+                           'old file with spaces.c',  'new file with spaces.c');
+    $this->runSingleRename('old file old file',
+                           'old file old',            'file',
+                           'old file old',            'file');
+  }
 }
diff --git a/src/parser/__tests__/diff/custom-prefixes-edit.gitdiff b/src/parser/__tests__/diff/custom-prefixes-edit.gitdiff
new file mode 100644
--- /dev/null
+++ b/src/parser/__tests__/diff/custom-prefixes-edit.gitdiff
@@ -0,0 +1,17 @@
+diff --git src/file dst/file
+index 711edb6..a8cd7be 100644
+--- src/file
++++ dst/file
+@@ -289,7 +289,9 @@ final class ArcanistDiffParser extends Phobject {
+       if (isset($match['type'])) {
+         if ($match['type'] == 'diff --git') {
+-          list($old, $new) = self::splitGitDiffPaths($match['oldnew']);
+-          $match['old'] = $old;
+-          $match['cur'] = $new;
++          $filename = self::splitGitDiffPaths($match['oldnew']);
++          if (isset($filename)) {
++            $match['old'] = $filename;
++            $match['cur'] = $filename;
++          }
+         }
+       }