diff --git a/docs/manifest-format.md b/docs/manifest-format.md
index 45fd615..c3bfcff 100644
--- a/docs/manifest-format.md
+++ b/docs/manifest-format.md
@@ -96,6 +96,7 @@
 
   <!ELEMENT remove-project EMPTY>
   <!ATTLIST remove-project name  CDATA #REQUIRED>
+  <!ATTLIST remove-project optional  CDATA #IMPLIED>
 
   <!ELEMENT repo-hooks EMPTY>
   <!ATTLIST repo-hooks in-project CDATA #REQUIRED>
@@ -393,6 +394,9 @@
 the user can remove a project, and possibly replace it with their
 own definition.
 
+Attribute `optional`: Set to true to ignore remove-project elements with no
+matching `project` element.
+
 ### Element repo-hooks
 
 NB: See the [practical documentation](./repo-hooks.md) for using repo hooks.
diff --git a/manifest_xml.py b/manifest_xml.py
index ab4be2f..be74bf4 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -918,19 +918,19 @@
       if node.nodeName == 'remove-project':
         name = self._reqatt(node, 'name')
 
-        if name not in self._projects:
+        if name in self._projects:
+          for p in self._projects[name]:
+            del self._paths[p.relpath]
+          del self._projects[name]
+
+          # If the manifest removes the hooks project, treat it as if it deleted
+          # the repo-hooks element too.
+          if self._repo_hooks_project and (self._repo_hooks_project.name == name):
+            self._repo_hooks_project = None
+        elif not XmlBool(node, 'optional', False):
           raise ManifestParseError('remove-project element specifies non-existent '
                                    'project: %s' % name)
 
-        for p in self._projects[name]:
-          del self._paths[p.relpath]
-        del self._projects[name]
-
-        # If the manifest removes the hooks project, treat it as if it deleted
-        # the repo-hooks element too.
-        if self._repo_hooks_project and (self._repo_hooks_project.name == name):
-          self._repo_hooks_project = None
-
   def _AddMetaProjectMirror(self, m):
     name = None
     m_url = m.GetRemote(m.remote.name).url
diff --git a/tests/test_manifest_xml.py b/tests/test_manifest_xml.py
index 55468b5..96ee4c4 100644
--- a/tests/test_manifest_xml.py
+++ b/tests/test_manifest_xml.py
@@ -638,3 +638,53 @@
     self.assertNotEqual(a, manifest_xml._Default())
     self.assertNotEqual(a, 123)
     self.assertNotEqual(a, None)
+
+
+class RemoveProjectElementTests(ManifestParseTestCase):
+  """Tests for <remove-project>."""
+
+  def test_remove_one_project(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+    self.assertEqual(manifest.projects, [])
+
+  def test_remove_one_project_one_remains(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <project name="yourproject" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+
+    self.assertEqual(len(manifest.projects), 1)
+    self.assertEqual(manifest.projects[0].name, 'yourproject')
+
+  def test_remove_one_project_doesnt_exist(self):
+    with self.assertRaises(manifest_xml.ManifestParseError):
+      manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+      manifest.projects
+
+  def test_remove_one_optional_project_doesnt_exist(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <remove-project name="myproject" optional="true" />
+</manifest>
+""")
+    self.assertEqual(manifest.projects, [])