diff --git a/hlink/configs/load_config.py b/hlink/configs/load_config.py
index 46b565a..d7baba8 100755
--- a/hlink/configs/load_config.py
+++ b/hlink/configs/load_config.py
@@ -7,11 +7,14 @@
 from typing import Any
 import json
 import toml
+import tomli
 
 from hlink.errors import UsageError
 
 
-def load_conf_file(conf_name: str) -> tuple[Path, dict[str, Any]]:
+def load_conf_file(
+    conf_name: str, *, use_legacy_toml_parser: bool = False
+) -> tuple[Path, dict[str, Any]]:
     """Flexibly load a config file.
 
     Given a path `conf_name`, look for a file at that path. If that file
@@ -20,8 +23,18 @@ def load_conf_file(conf_name: str) -> tuple[Path, dict[str, Any]]:
     name with a '.toml' extension added and load it if it exists. Then do the
     same for a file with a '.json' extension added.
 
+    `use_legacy_toml_parser` tells this function to use the legacy TOML library
+    which hlink used to use instead of the current default. This is provided
+    for backwards compatibility. Some previously written config files may
+    depend on bugs in the legacy TOML library, making it hard to migrate to the
+    new TOML v1.0 compliant parser. It is strongly recommended that new code
+    and config files use the default parser. Old code and config files should
+    also try to migrate to the default parser when possible.
+
     Args:
         conf_name: the file to look for
+        use_legacy_toml_parser: (Not Recommended) Use the legacy, buggy TOML
+        parser instead of the default parser.
 
     Returns:
         a tuple (absolute path to the config file, contents of the config file)
@@ -40,9 +53,19 @@ def load_conf_file(conf_name: str) -> tuple[Path, dict[str, Any]]:
 
     for file in existing_files:
         if file.suffix == ".toml":
-            with open(file) as f:
-                conf = toml.load(f)
-                return file.absolute(), conf
+            # Legacy support for using the "toml" library instead of "tomli".
+            #
+            # Eventually we should remove use_legacy_toml_parser and just use
+            # tomli or Python's standard library tomllib, which is available in
+            # Python 3.11+.
+            if use_legacy_toml_parser:
+                with open(file) as f:
+                    conf = toml.load(f)
+                    return file.absolute(), conf
+            else:
+                with open(file, "rb") as f:
+                    conf = tomli.load(f)
+                    return file.absolute(), conf
 
         if file.suffix == ".json":
             with open(file) as f:
diff --git a/hlink/tests/config_loader_test.py b/hlink/tests/config_loader_test.py
index b14e0b4..58ab53d 100644
--- a/hlink/tests/config_loader_test.py
+++ b/hlink/tests/config_loader_test.py
@@ -50,3 +50,18 @@ def test_load_conf_file_unrecognized_extension(tmp_path: Path) -> None:
         match="The file .+ exists, but it doesn't have a '.toml' or '.json' extension",
     ):
         load_conf_file(str(conf_file))
+
+
+def test_load_conf_file_json_legacy_parser(conf_dir_path: str) -> None:
+    """
+    The use_legacy_toml_parser argument does not affect json parsing.
+    """
+    conf_file = Path(conf_dir_path) / "test.json"
+    _, conf = load_conf_file(str(conf_file), use_legacy_toml_parser=True)
+    assert conf["id_column"] == "id"
+
+
+def test_load_conf_file_toml_legacy_parser(conf_dir_path: str) -> None:
+    conf_file = Path(conf_dir_path) / "test1.toml"
+    _, conf = load_conf_file(str(conf_file), use_legacy_toml_parser=True)
+    assert conf["id_column"] == "id-toml"
diff --git a/pyproject.toml b/pyproject.toml
index 3364294..deab3e9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@ dependencies = [
     "pyspark~=3.5.0",
     "scikit-learn>=1.1.0",
     "toml>=0.10.0",
+    "tomli>=2.0",
 ]
 
 [project.optional-dependencies]