diff --git a/singer_sdk/typing.py b/singer_sdk/typing.py
index 1a689b8fc..49baf0912 100644
--- a/singer_sdk/typing.py
+++ b/singer_sdk/typing.py
@@ -47,7 +47,7 @@
 
 import json
 import sys
-from typing import Any, Generic, Mapping, TypeVar, Union, cast
+from typing import Any, Generic, ItemsView, Mapping, TypeVar, Union, cast
 
 import sqlalchemy
 from jsonschema import validators
@@ -544,7 +544,7 @@ def __init__(
               }
             }
         """
-        self.wrapped: list[Property] = list(properties)
+        self.wrapped: dict[str, Property] = {prop.name: prop for prop in properties}
         self.additional_properties = additional_properties
         self.pattern_properties = pattern_properties
 
@@ -557,7 +557,7 @@ def type_dict(self) -> dict:  # type: ignore  # OK: @classproperty vs @property
         """
         merged_props = {}
         required = []
-        for w in self.wrapped:
+        for w in self.wrapped.values():
             merged_props.update(w.to_dict())
             if not w.optional:
                 required.append(w.name)
@@ -604,13 +604,13 @@ def type_dict(self) -> dict:  # type: ignore  # OK: @classproperty vs @property
 class PropertiesList(ObjectType):
     """Properties list. A convenience wrapper around the ObjectType class."""
 
-    def items(self) -> list[tuple[str, Property]]:
+    def items(self) -> ItemsView[str, Property]:
         """Get wrapped properties.
 
         Returns:
             List of (name, property) tuples.
         """
-        return [(p.name, p) for p in self.wrapped]
+        return self.wrapped.items()
 
     def append(self, property: Property) -> None:
         """Append a property to the property list.
@@ -618,7 +618,7 @@ def append(self, property: Property) -> None:
         Args:
             property: Property to add
         """
-        self.wrapped.append(property)
+        self.wrapped[property.name] = property
 
 
 def to_jsonschema_type(
diff --git a/tests/snapshots/jsonschema/required_duplicates.json b/tests/snapshots/jsonschema/required_duplicates.json
index aaa890002..5484f5247 100644
--- a/tests/snapshots/jsonschema/required_duplicates.json
+++ b/tests/snapshots/jsonschema/required_duplicates.json
@@ -25,7 +25,6 @@
     }
   },
   "required": [
-    "email",
     "email",
     "username"
   ]
diff --git a/tests/snapshots/jsonschema/required_duplicates_additional_properties.json b/tests/snapshots/jsonschema/required_duplicates_additional_properties.json
index c433255b1..17a773ded 100644
--- a/tests/snapshots/jsonschema/required_duplicates_additional_properties.json
+++ b/tests/snapshots/jsonschema/required_duplicates_additional_properties.json
@@ -25,7 +25,6 @@
     }
   },
   "required": [
-    "email",
     "email",
     "username"
   ],
diff --git a/tests/snapshots/jsonschema/required_duplicates_no_additional_properties.json b/tests/snapshots/jsonschema/required_duplicates_no_additional_properties.json
index fd65061f8..dcd44ca07 100644
--- a/tests/snapshots/jsonschema/required_duplicates_no_additional_properties.json
+++ b/tests/snapshots/jsonschema/required_duplicates_no_additional_properties.json
@@ -25,7 +25,6 @@
     }
   },
   "required": [
-    "email",
     "email",
     "username"
   ],