diff --git a/README.md b/README.md
index 3faed105..ed115bc7 100644
--- a/README.md
+++ b/README.md
@@ -387,6 +387,12 @@ with:
 
 Version tags will then be prefixed with the subpackage's name: `{PACKAGE}-v{VERSION}`, e.g., `SubpackageName-v0.2.3`. (For top-level packages, the default tag is simply `v{VERSION}`.) 
 
+**Note**: Using TagBot with a non-empty `subdir` will only work for Julia package versions
+registered using the official
+[Registrator](https://github.com/JuliaRegistries/Registrator.jl) (see also
+[#281](https://github.com/JuliaRegistries/TagBot/issues/281) and
+[#282](https://github.com/JuliaRegistries/TagBot/pull/282)).
+
 To tag releases from a monorepo containing multiple subpackages and an optional top-level package, set up a separate step for each package you want to tag. For example, to tag all three packages in the following repository,
 
 ```
diff --git a/tagbot/action/repo.py b/tagbot/action/repo.py
index f9ce14bb..ae9bb311 100644
--- a/tagbot/action/repo.py
+++ b/tagbot/action/repo.py
@@ -256,6 +256,18 @@ def _commit_sha_from_registry_pr(self, version: str, tree: str) -> Optional[str]
             logger.info("Registry PR body did not match")
             return None
         commit = self._repo.get_commit(m[1])
+        # Handle special case of tagging packages in a repo subdirectory, in which
+        # case the Julia package tree hash does not match the git commit tree hash
+        if self.__subdir:
+            arg = f"{commit.sha}:{self.__subdir}"
+            subdir_tree_hash = self._git.command("rev-parse", arg)
+            if subdir_tree_hash == tree:
+                return commit.sha
+            else:
+                msg = "Subdir tree SHA of commit from registry PR does not match"
+                logger.warning(msg)
+                return None
+        # Handle regular case (subdir is not set)
         if commit.commit.tree.sha == tree:
             return commit.sha
         else: