diff --git a/src/applications/repository/daemon/gitfetch/PhabricatorRepositoryGitFetchDaemon.php b/src/applications/repository/daemon/gitfetch/PhabricatorRepositoryGitFetchDaemon.php
index 74349961c4..cc42b714dc 100644
--- a/src/applications/repository/daemon/gitfetch/PhabricatorRepositoryGitFetchDaemon.php
+++ b/src/applications/repository/daemon/gitfetch/PhabricatorRepositoryGitFetchDaemon.php
@@ -37,6 +37,57 @@ final class PhabricatorRepositoryGitFetchDaemon
     PhabricatorRepository $repository,
     $local_path) {
 
+    // Run a bunch of sanity checks to detect people checking out repositories
+    // inside other repositories, making empty directories, pointing the local
+    // path at some random file or path, etc.
+
+    list($err, $stdout) = $repository->execLocalCommand(
+      'rev-parse --show-toplevel');
+
+    if ($err) {
+
+      // Try to raise a more tailored error message in the more common case
+      // of the user creating an empty directory. (We could try to remove it,
+      // but might not be able to, and it's much simpler to raise a good
+      // message than try to navigate those waters.)
+      if (is_dir($local_path)) {
+        $files = Filesystem::listDirectory($local_path, $include_hidden = true);
+        if (!$files) {
+          throw new Exception(
+            "Expected to find a git repository at '{$local_path}', but there ".
+            "is an empty directory there. Remove the directory: the daemon ".
+            "will run 'git clone' for you.");
+        }
+      }
+
+      throw new Exception(
+        "Expected to find a git repository at '{$local_path}', but there is ".
+        "a non-repository directory (with other stuff in it) there. Move or ".
+        "remove this directory (or reconfigure the repository to use a ".
+        "different directory), and then either clone a repository yourself ".
+        "or let the daemon do it.");
+    } else {
+      $repo_path = rtrim($stdout, "\n");
+
+      if (empty($repo_path)) {
+        throw new Exception(
+          "Expected to find a git repository at '{$local_path}', but ".
+          "there was no result from `git rev-parse --show-toplevel`. ".
+          "Something is misconfigured or broken. The git repository ".
+          "may be inside a '.git/' directory.");
+      }
+
+      if (!Filesystem::pathsAreEquivalent($repo_path, $local_path)) {
+        throw new Exception(
+          "Expected to find repo at '{$local_path}', but the actual ".
+          "git repository root for this directory is '{$repo_path}'. ".
+          "Something is misconfigured. The repository's 'Local Path' should ".
+          "be set to some place where the daemon can check out a working ".
+          "copy, and should not be inside another git repository.");
+      }
+    }
+
+
     // This is a local command, but needs credentials.
     $future = $repository->getRemoteCommandFuture('fetch --all --prune');
     $future->setCWD($local_path);
diff --git a/src/applications/repository/daemon/gitfetch/__init__.php b/src/applications/repository/daemon/gitfetch/__init__.php
index d59679cb9a..59c22675a8 100644
--- a/src/applications/repository/daemon/gitfetch/__init__.php
+++ b/src/applications/repository/daemon/gitfetch/__init__.php
@@ -9,5 +9,7 @@
 phutil_require_module('phabricator', 'applications/repository/constants/repositorytype');
 phutil_require_module('phabricator', 'applications/repository/daemon/pulllocal');
 
+phutil_require_module('phutil', 'filesystem');
+
 
 phutil_require_source('PhabricatorRepositoryGitFetchDaemon.php');