diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -381,6 +381,7 @@
     'DifferentialCloseConduitAPIMethod' => 'applications/differential/conduit/DifferentialCloseConduitAPIMethod.php',
     'DifferentialCommitMessageCustomField' => 'applications/differential/field/DifferentialCommitMessageCustomField.php',
     'DifferentialCommitMessageField' => 'applications/differential/field/DifferentialCommitMessageField.php',
+    'DifferentialCommitMessageFieldTestCase' => 'applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php',
     'DifferentialCommitMessageParser' => 'applications/differential/parser/DifferentialCommitMessageParser.php',
     'DifferentialCommitMessageParserTestCase' => 'applications/differential/parser/__tests__/DifferentialCommitMessageParserTestCase.php',
     'DifferentialCommitsField' => 'applications/differential/customfield/DifferentialCommitsField.php',
@@ -5030,6 +5031,7 @@
     'DifferentialCloseConduitAPIMethod' => 'DifferentialConduitAPIMethod',
     'DifferentialCommitMessageCustomField' => 'DifferentialCommitMessageField',
     'DifferentialCommitMessageField' => 'Phobject',
+    'DifferentialCommitMessageFieldTestCase' => 'PhabricatorTestCase',
     'DifferentialCommitMessageParser' => 'Phobject',
     'DifferentialCommitMessageParserTestCase' => 'PhabricatorTestCase',
     'DifferentialCommitsField' => 'DifferentialCustomField',
diff --git a/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php b/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php
--- a/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php
+++ b/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php
@@ -18,8 +18,25 @@
   }
 
   public function parseFieldValue($value) {
-    // If the value is just "D123" or similar, parse the ID from it directly.
+    // If the complete commit message we are parsing has unrecognized custom
+    // fields at the end, they can end up parsed into the field value for this
+    // field. For example, if the message looks like this:
+
+    // Differential Revision: xyz
+    // Some-Other-Field: abc
+
+    // ...we will receive "xyz\nSome-Other-Field: abc" as the field value for
+    // this field. Ideally, the install would define these fields so they can
+    // parse formally, but we can reasonably assume that only the first line
+    // of any value we encounter actually contains a revision identifier, so
+    // start by throwing away any other lines.
+
     $value = trim($value);
+    $value = phutil_split_lines($value, false);
+    $value = head($value);
+    $value = trim($value);
+
+    // If the value is just "D123" or similar, parse the ID from it directly.
     $matches = null;
     if (preg_match('/^[dD]([1-9]\d*)\z/', $value, $matches)) {
       return (int)$matches[1];
diff --git a/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php b/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php
@@ -0,0 +1,30 @@
+<?php
+
+final class DifferentialCommitMessageFieldTestCase
+  extends PhabricatorTestCase {
+
+  public function testRevisionCommitMessageFieldParsing() {
+    $base_uri = 'https://www.example.com/';
+
+    $tests = array(
+      'D123' => 123,
+      'd123' => 123,
+      "  \n  d123 \n " => 123,
+      "D123\nSome-Custom-Field: The End" => 123,
+      "{$base_uri}D123" => 123,
+      "{$base_uri}D123\nSome-Custom-Field: The End" => 123,
+    );
+
+    $env = PhabricatorEnv::beginScopedEnv();
+    $env->overrideEnvConfig('phabricator.base-uri', $base_uri);
+
+    foreach ($tests as $input => $expect) {
+      $actual = id(new DifferentialRevisionIDCommitMessageField())
+        ->parseFieldValue($input);
+      $this->assertEqual($expect, $actual, pht('Parse of: %s', $input));
+    }
+
+    unset($env);
+  }
+
+}
diff --git a/src/applications/differential/parser/DifferentialCommitMessageParser.php b/src/applications/differential/parser/DifferentialCommitMessageParser.php
--- a/src/applications/differential/parser/DifferentialCommitMessageParser.php
+++ b/src/applications/differential/parser/DifferentialCommitMessageParser.php
@@ -155,7 +155,10 @@
     $field = $key_title;
 
     $seen = array();
-    $lines = explode("\n", trim($corpus));
+
+    $lines = trim($corpus);
+    $lines = phutil_split_lines($lines, false);
+
     $field_map = array();
     foreach ($lines as $key => $line) {
       $match = null;