diff --git a/lib/spack/llnl/util/filesystem.py b/lib/spack/llnl/util/filesystem.py
index f280534852b..35c85ba3ae9 100644
--- a/lib/spack/llnl/util/filesystem.py
+++ b/lib/spack/llnl/util/filesystem.py
@@ -75,7 +75,6 @@
     "install_tree",
     "is_exe",
     "join_path",
-    "last_modification_time_recursive",
     "library_extensions",
     "mkdirp",
     "partition_path",
@@ -1470,15 +1469,36 @@ def set_executable(path):
 
 
 @system_path_filter
-def last_modification_time_recursive(path):
-    path = os.path.abspath(path)
-    times = [os.stat(path).st_mtime]
-    times.extend(
-        os.lstat(os.path.join(root, name)).st_mtime
-        for root, dirs, files in os.walk(path)
-        for name in dirs + files
-    )
-    return max(times)
+def recursive_mtime_greater_than(path: str, time: float) -> bool:
+    """Returns true if any file or dir recursively under `path` has mtime greater than `time`."""
+    # use bfs order to increase likelihood of early return
+    queue: Deque[str] = collections.deque()
+
+    if os.stat(path).st_mtime > time:
+        return True
+
+    while queue:
+        current = queue.popleft()
+
+        try:
+            entries = os.scandir(current)
+        except OSError:
+            continue
+
+        with entries:
+            for entry in entries:
+                try:
+                    st = entry.stat(follow_symlinks=False)
+                except OSError:
+                    continue
+
+                if st.st_mtime > time:
+                    return True
+
+                if entry.is_dir(follow_symlinks=False):
+                    queue.append(entry.path)
+
+    return False
 
 
 @system_path_filter
diff --git a/lib/spack/spack/package_base.py b/lib/spack/spack/package_base.py
index b6dde08638c..0bfd0144989 100644
--- a/lib/spack/spack/package_base.py
+++ b/lib/spack/spack/package_base.py
@@ -1099,14 +1099,14 @@ def update_external_dependencies(self, extendee_spec=None):
         """
         pass
 
-    def detect_dev_src_change(self):
+    def detect_dev_src_change(self) -> bool:
         """
         Method for checking for source code changes to trigger rebuild/reinstall
         """
         dev_path_var = self.spec.variants.get("dev_path", None)
         _, record = spack.store.STORE.db.query_by_spec_hash(self.spec.dag_hash())
-        mtime = fsys.last_modification_time_recursive(dev_path_var.value)
-        return mtime > record.installation_time
+        assert dev_path_var and record, "dev_path variant and record must be present"
+        return fsys.recursive_mtime_greater_than(dev_path_var.value, record.installation_time)
 
     def all_urls_for_version(self, version: StandardVersion) -> List[str]:
         """Return all URLs derived from version_urls(), url, urls, and