diff --git a/src/plumpy/ports.py b/src/plumpy/ports.py
index 39c87e77..1e4c3375 100644
--- a/src/plumpy/ports.py
+++ b/src/plumpy/ports.py
@@ -730,18 +730,22 @@ def validate_dynamic_ports(
         :return: if invalid returns a string with the reason for the validation failure, otherwise None
         :rtype: typing.Optional[str]
         """
-        breadcrumbs = (*breadcrumbs, self.name)
-
         if port_values and not self.dynamic:
             msg = f'Unexpected ports {port_values}, for a non dynamic namespace'
+            return PortValidationError(msg, breadcrumbs_to_port((*breadcrumbs, self.name)))
+
+        if self.valid_type is None:
+            return None
+
+        if isinstance(port_values, dict):
+            for key, value in port_values.items():
+                result = self.validate_dynamic_ports(value, (*breadcrumbs, self.name, key))
+                if result is not None:
+                    return result
+        elif not isinstance(port_values, self.valid_type):
+            msg = f'Invalid type {type(port_values)} for dynamic port value: expected {self.valid_type}'
             return PortValidationError(msg, breadcrumbs_to_port(breadcrumbs))
 
-        if self.valid_type is not None:
-            valid_type = self.valid_type
-            for port_name, port_value in port_values.items():
-                if not isinstance(port_value, valid_type):
-                    msg = f'Invalid type {type(port_value)} for dynamic port value: expected {valid_type}'
-                    return PortValidationError(msg, breadcrumbs_to_port(breadcrumbs + (port_name,)))
         return None
 
     @staticmethod
diff --git a/test/test_port.py b/test/test_port.py
index 029c109c..55ddbe66 100644
--- a/test/test_port.py
+++ b/test/test_port.py
@@ -249,9 +249,14 @@ def test_port_namespace_set_valid_type(self):
         self.assertIsNone(self.port_namespace.valid_type)
 
     def test_port_namespace_validate(self):
-        """Check that validating of sub namespaces works correctly"""
+        """Check that validating of sub namespaces works correctly.
+
+        By setting a valid type on a port namespace, it automatically becomes dynamic. Port namespaces that are dynamic
+        should accept arbitrarily nested input and should validate, as long as all leaf values satisfy the `valid_type`.
+        """
         port_namespace_sub = self.port_namespace.create_port_namespace('sub.space')
         port_namespace_sub.valid_type = int
+        assert port_namespace_sub.dynamic
 
         # Check that passing a non mapping type raises
         validation_error = self.port_namespace.validate(5)
@@ -261,7 +266,12 @@ def test_port_namespace_validate(self):
         validation_error = self.port_namespace.validate({'sub': {'space': {'output': 5}}})
         self.assertIsNone(validation_error)
 
-        # Invalid input
+        # Valid input: `sub.space` is dynamic, so should allow arbitrarily nested namespaces as long as the leaf values
+        # match the valid type, which is `int` in this example.
+        validation_error = self.port_namespace.validate({'sub': {'space': {'output': {'invalid': 5}}}})
+        self.assertIsNone(validation_error)
+
+        # Invalid input - the value in ``space`` is not ``int`` but a ``str``
         validation_error = self.port_namespace.validate({'sub': {'space': {'output': '5'}}})
         self.assertIsNotNone(validation_error)