diff --git a/hyperpyyaml/core.py b/hyperpyyaml/core.py
index 6900792..42fea40 100644
--- a/hyperpyyaml/core.py
+++ b/hyperpyyaml/core.py
@@ -186,6 +186,10 @@ def load_hyperpyyaml(
     ruamel.yaml.constructor.BaseConstructor.construct_object.__defaults__ = (
         True,
     )  # deep=True
+    # ruamel.yaml >= 0.19 added max_depth checking in the composer,
+    # but the legacy Loader class does not define this attribute.
+    if not hasattr(loader, 'max_depth'):
+        loader.max_depth = 0
     hparams = yaml.load(yaml_stream, Loader=loader)
     # Change back to normal default:
     yaml.constructor.BaseConstructor.construct_object.__defaults__ = (
diff --git a/setup.py b/setup.py
index 034aa53..c16d7c1 100644
--- a/setup.py
+++ b/setup.py
@@ -18,5 +18,5 @@
         "License :: OSI Approved :: Apache Software License",
     ],
     packages=["hyperpyyaml"],
-    install_requires=["pyyaml>=5.1", "ruamel.yaml>=0.17.28,<0.19.0"],
+    install_requires=["pyyaml>=5.1", "ruamel.yaml>=0.17.28"],
 )