diff --git a/meta/classes/externalsrc.bbclass b/meta/classes/externalsrc.bbclass
index 8136d25cb1..880556b834 100644
--- a/meta/classes/externalsrc.bbclass
+++ b/meta/classes/externalsrc.bbclass
@@ -211,8 +211,8 @@ def srctree_hash_files(d, srcdir=None):
     try:
         git_dir = os.path.join(s_dir,
             subprocess.check_output(['git', '-C', s_dir, 'rev-parse', '--git-dir'], stderr=subprocess.DEVNULL).decode("utf-8").rstrip())
-        top_git_dir = os.path.join(s_dir, subprocess.check_output(['git', '-C', d.getVar("TOPDIR"), 'rev-parse', '--git-dir'],
-            stderr=subprocess.DEVNULL).decode("utf-8").rstrip())
+        top_git_dir = os.path.join(d.getVar("TOPDIR"),
+            subprocess.check_output(['git', '-C', d.getVar("TOPDIR"), 'rev-parse', '--git-dir'], stderr=subprocess.DEVNULL).decode("utf-8").rstrip())
         if git_dir == top_git_dir:
             git_dir = None
     except subprocess.CalledProcessError: