diff --git a/tools/cargo-check-external-types/Cargo.lock b/tools/cargo-check-external-types/Cargo.lock
index 5eeb438344cbd2fa2ae2d28b8ffe96d8bd680faa..c034a93937cb5b84ae658970eabc6dac72444188 100644
--- a/tools/cargo-check-external-types/Cargo.lock
+++ b/tools/cargo-check-external-types/Cargo.lock
@@ -51,7 +51,7 @@ dependencies = [
 
 [[package]]
 name = "cargo-check-external-types"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "anyhow",
  "cargo_metadata",
diff --git a/tools/smithy-rs-tool-common/Cargo.toml b/tools/smithy-rs-tool-common/Cargo.toml
index c370a6e4031131d038db276837bbb5e9397f32d4..e3b6e870603755e8c2ee07caa41e979ff86b692f 100644
--- a/tools/smithy-rs-tool-common/Cargo.toml
+++ b/tools/smithy-rs-tool-common/Cargo.toml
@@ -27,3 +27,6 @@ serde_json = "1"
 tokio = { version = "1", features = ["rt", "macros"], optional = true }
 toml = { version = "0.5.8", features = ["preserve_order"] }
 tracing = "0.1"
+
+[dev-dependencies]
+tempfile = "3.3.0"
diff --git a/tools/smithy-rs-tool-common/src/git.rs b/tools/smithy-rs-tool-common/src/git.rs
index 22b670e181bb1067b841ccd422062ce6623118ea..b22543f0ab5ceea41f6c5b20d9b0d450a4ac7478 100644
--- a/tools/smithy-rs-tool-common/src/git.rs
+++ b/tools/smithy-rs-tool-common/src/git.rs
@@ -151,7 +151,7 @@ pub struct GitCLI {
 
 impl GitCLI {
     pub fn new(repo_path: &Path) -> Result<Self> {
-        if !repo_path.join(".git").is_dir() {
+        if !repo_path.join(".git").exists() {
             bail!("{:?} is not a git repository", repo_path);
         }
         Ok(Self {
@@ -429,7 +429,8 @@ fn log_command(command: Command) -> Command {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::env;
+    use std::{env, fs};
+    use tempfile::TempDir;
 
     fn bin_path(script: &'static str) -> PathBuf {
         env::current_dir()
@@ -616,4 +617,26 @@ mod tests {
             .squash_merge("some-dev", "some-email@example.com", "test-branch-name")
             .expect("successful invocation");
     }
+
+    #[test]
+    fn repository_root_check() {
+        let tmp_dir = TempDir::new().unwrap();
+        GitCLI::new(tmp_dir.path())
+            .err()
+            .expect("repository root check should fail");
+
+        fs::create_dir(tmp_dir.path().join(".git")).unwrap();
+        GitCLI::new(tmp_dir.path()).expect("repository root check should succeed");
+    }
+
+    #[test]
+    fn repository_root_check_works_for_git_submodules() {
+        let tmp_dir = TempDir::new().unwrap();
+        GitCLI::new(tmp_dir.path())
+            .err()
+            .expect("repository root check should fail");
+
+        fs::write(tmp_dir.path().join(".git"), "gitdir: some/fake/path").unwrap();
+        GitCLI::new(tmp_dir.path()).expect("repository root check should succeed");
+    }
 }