diff --git a/python/BUILD.bazel b/python/BUILD.bazel
index fc003335..df169761 100644
--- a/python/BUILD.bazel
+++ b/python/BUILD.bazel
@@ -158,6 +158,14 @@ py_test(
     ],
 )
 
+py_test(
+    name = "convert_pbn_test",
+    size = "small",
+    main = "tests/test_convert_pbn.py",
+    srcs = ["tests/test_convert_pbn.py"],
+    deps = ["//python/examples:dd_table_for_deal_lib"],
+)
+
 py_wheel(
     name = "dds3_wheel",
     distribution = "dds3",
diff --git a/python/examples/BUILD.bazel b/python/examples/BUILD.bazel
index 39e7c152..8ef2d568 100644
--- a/python/examples/BUILD.bazel
+++ b/python/examples/BUILD.bazel
@@ -1,8 +1,16 @@
-load("@rules_python//python:defs.bzl", "py_binary")
+load("@rules_python//python:defs.bzl", "py_binary", "py_library")
+
+py_library(
+    name = "dd_table_for_deal_lib",
+    srcs = ["dd_table_for_deal.py"],
+    imports = ["."],
+    deps = ["//python:dds3_lib"],
+    visibility = ["//python:__pkg__"],
+)
 
 py_binary(
     name = "dd_table_for_deal",
     srcs = ["dd_table_for_deal.py"],
     main = "dd_table_for_deal.py",
-    deps = ["//python:dds3_lib"],
+    deps = [":dd_table_for_deal_lib"],
 )
diff --git a/python/examples/dd_table_for_deal.py b/python/examples/dd_table_for_deal.py
index 53652505..1498841d 100644
--- a/python/examples/dd_table_for_deal.py
+++ b/python/examples/dd_table_for_deal.py
@@ -113,10 +113,11 @@ def _convert_pbn(pbn_deal: str) -> list[list[int]]:
     bp = 0
     while (
         bp < 3
+        and bp < len(pbn_deal)
         and pbn_deal[bp] not in "NWESnwes"
     ):
         bp += 1
-    if bp >= 3:
+    if bp >= 3 or bp >= len(pbn_deal):
         return remain
 
     first = {"N": 0, "E": 1, "S": 2, "W": 3}[pbn_deal[bp].upper()]
diff --git a/python/tests/test_convert_pbn.py b/python/tests/test_convert_pbn.py
new file mode 100644
index 00000000..905b9430
--- /dev/null
+++ b/python/tests/test_convert_pbn.py
@@ -0,0 +1,32 @@
+"""Tests for PBN-to-bitmask conversion in dd_table_for_deal."""
+
+import unittest
+
+from dd_table_for_deal import _convert_pbn
+
+_EMPTY_REMAIN = [[0] * 4 for _ in range(4)]
+
+_EXAMPLE_DEAL = (
+    "N:73.QJT.AQ54.T752 QT6.876.KJ9.AQ84 "
+    "5.A95432.7632.K6 AKJ9842.K.T8.J93"
+)
+
+
+class ConvertPbnTest(unittest.TestCase):
+    def test_short_deal_strings_return_empty_remain(self) -> None:
+        """Short or malformed PBN strings must not raise IndexError."""
+        for deal in ("", "N", "N:", "12", "abc"):
+            with self.subTest(deal=deal):
+                self.assertEqual(_convert_pbn(deal), _EMPTY_REMAIN)
+
+    def test_valid_deal_parses_card_bitmasks(self) -> None:
+        remain = _convert_pbn(_EXAMPLE_DEAL)
+
+        # North's spades: 73
+        self.assertEqual(remain[0][0], 0x0080 | 0x0008)
+        # North's hearts: QJT
+        self.assertEqual(remain[0][1], 0x1000 | 0x0800 | 0x0400)
+
+
+if __name__ == "__main__":
+    unittest.main()