diff --git a/src/borg/hashindex.pyx b/src/borg/hashindex.pyx
index 916df65ed..44f1fcbe1 100644
--- a/src/borg/hashindex.pyx
+++ b/src/borg/hashindex.pyx
@@ -237,8 +237,8 @@ cdef class NSIndex(IndexBase):
         iter.index = self.index
         if marker:
             key = hashindex_get(self.index, <unsigned char *>marker)
-            if marker is None:
-                raise IndexError
+            if not key:
+                raise KeyError("marker not found")
             iter.key = key - self.key_size
         return iter
 
@@ -354,8 +354,8 @@ cdef class ChunkIndex(IndexBase):
         iter.index = self.index
         if marker:
             key = hashindex_get(self.index, <unsigned char *>marker)
-            if marker is None:
-                raise IndexError
+            if not key:
+                raise KeyError("marker not found")
             iter.key = key - self.key_size
         return iter
 
diff --git a/src/borg/testsuite/hashindex_pytest.py b/src/borg/testsuite/hashindex_pytest.py
new file mode 100644
index 000000000..4a82775c7
--- /dev/null
+++ b/src/borg/testsuite/hashindex_pytest.py
@@ -0,0 +1,30 @@
+import pytest
+from borg.hashindex import NSIndex, ChunkIndex
+
+def test_nsindex_iteritems_marker():
+    nsindex = NSIndex()
+    nsindex[b'\xbb'*32] = (123, 456)
+    nsindex[b'\xaa'*32] = (234, 567)
+
+    # marker exists
+    items = list(nsindex.iteritems(marker=b'\xbb'*32))
+    assert len(items) == 1
+    assert items[0][0] == b'\xaa'*32
+
+    # marker does not exist
+    with pytest.raises(KeyError, match="marker not found"):
+        list(nsindex.iteritems(marker=b'\xcc'*32))
+
+def test_chunkindex_iteritems_marker():
+    chunkindex = ChunkIndex()
+    chunkindex[b'\xbb'*32] = (1, 100, 50)
+    chunkindex[b'\xaa'*32] = (1, 200, 100)
+
+    # marker exists
+    items = list(chunkindex.iteritems(marker=b'\xbb'*32))
+    assert len(items) == 1
+    assert items[0][0] == b'\xaa'*32
+
+    # marker does not exist
+    with pytest.raises(KeyError, match="marker not found"):
+        list(chunkindex.iteritems(marker=b'\xcc'*32))