diff --git a/gclient_eval.py b/gclient_eval.py
index 93fd2a8b5..aac3535f0 100644
--- a/gclient_eval.py
+++ b/gclient_eval.py
@@ -666,7 +666,13 @@ def SetRevision(gclient_dict, dep_name, new_revision):
       SetVar(gclient_dict, var_name, new_revision)
     else:
       if '@' in node.s:
+        # '@' is part of the last string, which we want to modify. Discard
+        # whatever was after the '@' and put the new revision in its place.
         new_revision = node.s.split('@')[0] + '@' + new_revision
+      elif '@' not in dep_dict[dep_key]:
+        # '@' is not part of the URL at all. This mean the dependency is
+        # unpinned and we should pin it.
+        new_revision = node.s + '@' + new_revision
       _UpdateAstString(tokens, node, new_revision)
       dep_dict.SetNode(dep_key, new_revision, node)
 
diff --git a/tests/gclient_eval_unittest.py b/tests/gclient_eval_unittest.py
index 9316e3502..c7896b362 100755
--- a/tests/gclient_eval_unittest.py
+++ b/tests/gclient_eval_unittest.py
@@ -504,6 +504,20 @@ class SetRevisionTest(unittest.TestCase):
     ]
     self.assert_changes_revision(before, after)
 
+  def test_pins_revision(self):
+    before = [
+        'deps = {',
+        '  "src/dep": "https://example.com/dep.git",',
+        '}',
+    ]
+    after = [
+        'deps = {',
+        '  "src/dep": "https://example.com/dep.git@deadfeed",',
+        '}',
+    ]
+    self.assert_changes_revision(before, after)
+
+
   def test_preserves_formatting(self):
     before = [
         'vars = {',