diff --git a/recipe_modules/merge_roll/api.py b/recipe_modules/merge_roll/api.py
index cb052be..4845e20 100644
--- a/recipe_modules/merge_roll/api.py
+++ b/recipe_modules/merge_roll/api.py
@@ -50,7 +50,7 @@
         self,
         checkout: checkout_api.CheckoutContext,
         new_revision: str,
-    ) -> RevisionChange:
+    ) -> RevisionChange | None:
         """Prepares and returns a RevisionChange object for a merge.
 
         A `finalize` function is created that, when called, will merge the
@@ -62,16 +62,25 @@
 
         Returns:
             A `RevisionChange` object containing the old and new revisions,
-            and a `finalize` callable to apply the update.
+            and a `finalize` callable to apply the update, or None if there's
+            nothing to merge.
         """
 
         with self.m.context(cwd=checkout.top):
-            first_new_commit = self.m.git.cherry(
-                source=new_revision,
-                destination='main',
-            )[-1].commit
+            self.m.git.fetch(checkout.options.remote, new_revision)
 
-            old_revision = self.m.git.rev_parse(f'{first_new_commit}~1')
+            new_commits: list[str] = []
+            for pair in self.m.git.cherry(
+                source=new_revision,
+                destination='HEAD',
+            ):
+                if not pair.has_equivalent:
+                    new_commits.append(pair.commit)
+
+            if not new_commits:
+                return None  # pragma: no cover
+
+            old_revision = self.m.git.rev_parse(f'{new_commits[0]}~1')
 
         def finalize() -> None:
             with self.m.context(cwd=checkout.top):
@@ -103,6 +112,9 @@
                 new_revision,
             )
 
+            if not change:
+                return []  # pragma: no cover
+
             try:
                 roll = self.m.git_roll_util.get_roll(
                     repo_url=checkout.options.remote,
diff --git a/recipes/roller.expected/mega.json b/recipes/roller.expected/mega.json
index f63144e..8c84ecf 100644
--- a/recipes/roller.expected/mega.json
+++ b/recipes/roller.expected/mega.json
@@ -7716,8 +7716,46 @@
   {
     "cmd": [
       "git",
+      "fetch",
+      "--jobs",
+      "4",
+      "https://pigweed.googlesource.com/pigweed/pigweed",
+      "h3ll0"
+    ],
+    "cwd": "[START_DIR]/co",
+    "env": {
+      "GIT_ADVICE": "0",
+      "GIT_CONFIG_COUNT": "3",
+      "GIT_CONFIG_KEY_0": "gc.auto",
+      "GIT_CONFIG_KEY_1": "gc.autoDetach",
+      "GIT_CONFIG_KEY_2": "gc.autoPackLimit",
+      "GIT_CONFIG_VALUE_0": "0",
+      "GIT_CONFIG_VALUE_1": "0",
+      "GIT_CONFIG_VALUE_2": "0"
+    },
+    "luci_context": {
+      "realm": {
+        "name": "project:ci"
+      },
+      "resultdb": {
+        "current_invocation": {
+          "name": "invocations/build:8945511751514863184",
+          "update_token": "token"
+        },
+        "hostname": "rdbhost"
+      }
+    },
+    "name": "staging.git fetch",
+    "timeout": 1200.0,
+    "~followup_annotations": [
+      "@@@STEP_NEST_LEVEL@1@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "git",
       "cherry",
-      "main",
+      "HEAD",
       "h3ll0"
     ],
     "cwd": "[START_DIR]/co",
diff --git a/recipes/roller.expected/noop.json b/recipes/roller.expected/noop.json
index 991139e..940556d 100644
--- a/recipes/roller.expected/noop.json
+++ b/recipes/roller.expected/noop.json
@@ -3600,8 +3600,34 @@
   {
     "cmd": [
       "git",
+      "fetch",
+      "--jobs",
+      "4",
+      "https://pigweed.googlesource.com/pigweed/pigweed",
+      "h3ll0"
+    ],
+    "cwd": "[START_DIR]/co",
+    "env": {
+      "GIT_ADVICE": "0",
+      "GIT_CONFIG_COUNT": "3",
+      "GIT_CONFIG_KEY_0": "gc.auto",
+      "GIT_CONFIG_KEY_1": "gc.autoDetach",
+      "GIT_CONFIG_KEY_2": "gc.autoPackLimit",
+      "GIT_CONFIG_VALUE_0": "0",
+      "GIT_CONFIG_VALUE_1": "0",
+      "GIT_CONFIG_VALUE_2": "0"
+    },
+    "name": "staging.git fetch",
+    "timeout": 1200.0,
+    "~followup_annotations": [
+      "@@@STEP_NEST_LEVEL@1@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "git",
       "cherry",
-      "main",
+      "HEAD",
       "h3ll0"
     ],
     "cwd": "[START_DIR]/co",