diff --git a/src/borgstore/backends/posixfs.py b/src/borgstore/backends/posixfs.py
index d61f931..a39a964 100644
--- a/src/borgstore/backends/posixfs.py
+++ b/src/borgstore/backends/posixfs.py
@@ -10,7 +10,8 @@
 import tempfile
 
 from ._base import BackendBase, ItemInfo, validate_name
-from .errors import BackendAlreadyExists, BackendDoesNotExist, BackendMustNotBeOpen, BackendMustBeOpen, ObjectNotFound
+from .errors import BackendError, BackendAlreadyExists, BackendDoesNotExist, BackendMustNotBeOpen, BackendMustBeOpen
+from .errors import ObjectNotFound
 from ..constants import TMP_SUFFIX
 
 
@@ -37,9 +38,13 @@ def create(self):
         if self.opened:
             raise BackendMustNotBeOpen()
         try:
-            self.base_path.mkdir()
-        except FileExistsError:
-            raise BackendAlreadyExists(f"posixfs storage base path already exists: {self.base_path}")
+            # we accept an already existing directory, but we do not create parent dirs:
+            self.base_path.mkdir(exist_ok=True, parents=False)
+        except FileNotFoundError:
+            raise BackendError(f"posixfs storage base path's parent directory does not exist: {self.base_path}")
+        contents = list(self.base_path.iterdir())
+        if contents:
+            raise BackendAlreadyExists(f"posixfs storage base path is not empty: {self.base_path}")
 
     def destroy(self):
         if self.opened:
diff --git a/src/borgstore/backends/sftp.py b/src/borgstore/backends/sftp.py
index 5f3404f..8c1ead6 100644
--- a/src/borgstore/backends/sftp.py
+++ b/src/borgstore/backends/sftp.py
@@ -11,7 +11,8 @@
 import paramiko
 
 from ._base import BackendBase, ItemInfo, validate_name
-from .errors import BackendMustBeOpen, BackendMustNotBeOpen, BackendDoesNotExist, BackendAlreadyExists, ObjectNotFound
+from .errors import BackendError, BackendMustBeOpen, BackendMustNotBeOpen, BackendDoesNotExist, BackendAlreadyExists
+from .errors import ObjectNotFound
 from ..constants import TMP_SUFFIX
 
 
@@ -91,9 +92,16 @@ def create(self):
             raise BackendMustNotBeOpen()
         self._connect()
         try:
-            self._mkdir(self.base_path, parents=False, exist_ok=False)
-        except (FileExistsError, IOError):
-            raise BackendAlreadyExists(f"sftp storage base path already exists: {self.base_path}")
+            try:
+                # we accept an already existing directory, but we do not create parent dirs:
+                self._mkdir(self.base_path, exist_ok=True, parents=False)
+            except FileNotFoundError:
+                raise BackendError(f"sftp storage base path's parent directory does not exist: {self.base_path}")
+            contents = list(self.client.listdir(self.base_path))
+            if contents:
+                raise BackendAlreadyExists(f"sftp storage base path is not empty: {self.base_path}")
+        except IOError as err:
+            raise BackendError(f"sftp storage I/O error: {err}")
         finally:
             self._disconnect()
 
diff --git a/tests/test_backends.py b/tests/test_backends.py
index c37a45d..09d469c 100644
--- a/tests/test_backends.py
+++ b/tests/test_backends.py
@@ -324,6 +324,9 @@ def test_load_partial(tested_backends, request):
 
 def test_already_exists(tested_backends, request):
     backend = get_backend_from_fixture(tested_backends, request)
+    with backend as _backend:
+        _backend.store("key", b"value")  # make the backend "not empty"
+    # the backend must reject (re-)creation if there is already something at that place:
     with pytest.raises(BackendAlreadyExists):
         backend.create()