diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a6369094..c83a7ac3b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 - Added new attribute "dimension_labels" on `DatasetBuilder` which specifies the names of the dimensions used in the
 dataset based on the shape of the dataset data and the dimension names in the spec for the data type. This attribute
 is available on build (during the write process), but not on read of a dataset from a file. @rly [#1081](https://github.com/hdmf-dev/hdmf/pull/1081)
+- Speed up loading namespaces by skipping register_type when already registered. @magland [#1102](https://github.com/hdmf-dev/hdmf/pull/1102)
 
 ## HDMF 3.14.2 (July 7, 2024)
 
diff --git a/src/hdmf/spec/namespace.py b/src/hdmf/spec/namespace.py
index a2ae0bd37..f0417175f 100644
--- a/src/hdmf/spec/namespace.py
+++ b/src/hdmf/spec/namespace.py
@@ -466,15 +466,19 @@ def __load_namespace(self, namespace, reader, resolve=True):
         return included_types
 
     def __register_type(self, ndt, inc_ns, catalog, registered_types):
-        spec = inc_ns.get_spec(ndt)
-        spec_file = inc_ns.catalog.get_spec_source_file(ndt)
-        self.__register_dependent_types(spec, inc_ns, catalog, registered_types)
-        if isinstance(spec, DatasetSpec):
-            built_spec = self.dataset_spec_cls.build_spec(spec)
+        if ndt in registered_types:
+            # already registered
+            pass
         else:
-            built_spec = self.group_spec_cls.build_spec(spec)
-        registered_types.add(ndt)
-        catalog.register_spec(built_spec, spec_file)
+            spec = inc_ns.get_spec(ndt)
+            spec_file = inc_ns.catalog.get_spec_source_file(ndt)
+            self.__register_dependent_types(spec, inc_ns, catalog, registered_types)
+            if isinstance(spec, DatasetSpec):
+                built_spec = self.dataset_spec_cls.build_spec(spec)
+            else:
+                built_spec = self.group_spec_cls.build_spec(spec)
+            registered_types.add(ndt)
+            catalog.register_spec(built_spec, spec_file)
 
     def __register_dependent_types(self, spec, inc_ns, catalog, registered_types):
         """Ensure that classes for all types used by this type are registered