diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index c323ecf..10f5a9a 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -21,6 +21,7 @@ Notes:
 """
 from typing import IO, cast, Any
 from collections.abc import Iterable, Mapping, Callable
+from types import MappingProxyType
 import io
 import mmap
 import logging
@@ -52,6 +53,8 @@ path_cap_map = {
     4: Path.Cap.SquareCustom,
     }
 
+RO_EMPTY_DICT: Mapping[int, bytes] = MappingProxyType({})
+
 
 def rint_cast(val: ArrayLike) -> NDArray[numpy.int32]:
     return numpy.rint(val).astype(numpy.int32)
@@ -399,11 +402,15 @@ def _mrefs_to_grefs(refs: dict[str | None, list[Ref]]) -> list[klamath.library.R
     return grefs
 
 
-def _properties_to_annotations(properties: dict[int, bytes]) -> annotations_t:
+def _properties_to_annotations(properties: Mapping[int, bytes]) -> annotations_t:
+    if not properties:
+        return None
     return {str(k): [v.decode()] for k, v in properties.items()}
 
 
-def _annotations_to_properties(annotations: annotations_t, max_len: int = 126) -> dict[int, bytes]:
+def _annotations_to_properties(annotations: annotations_t, max_len: int = 126) -> Mapping[int, bytes]:
+    if annotations is None:
+        return RO_EMPTY_DICT
     cum_len = 0
     props = {}
     for key, vals in annotations.items():
diff --git a/masque/file/oasis.py b/masque/file/oasis.py
index e64bb4c..642ad44 100644
--- a/masque/file/oasis.py
+++ b/masque/file/oasis.py
@@ -671,6 +671,8 @@ def repetition_masq2fata(
 
 def annotations_to_properties(annotations: annotations_t) -> list[fatrec.Property]:
     #TODO determine is_standard based on key?
+    if annotations is None:
+        return []
     properties = []
     for key, values in annotations.items():
         vals = [AString(v) if isinstance(v, str) else v
diff --git a/masque/pattern.py b/masque/pattern.py
index 5bf030a..f77c64f 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -332,7 +332,7 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
             ))
 
         self.ports = dict(sorted(self.ports.items()))
-        self.annotations = dict(sorted(self.annotations.items()))
+        self.annotations = dict(sorted(self.annotations.items())) if self.annotations is not None else None
 
         return self
 
@@ -354,10 +354,13 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
         for layer, lseq in other_pattern.labels.items():
             self.labels[layer].extend(lseq)
 
-        annotation_conflicts = set(self.annotations.keys()) & set(other_pattern.annotations.keys())
-        if annotation_conflicts:
-            raise PatternError(f'Annotation keys overlap: {annotation_conflicts}')
-        self.annotations.update(other_pattern.annotations)
+        if other_pattern.annotations is not None:
+            if self.annotations is None:
+                self.annotations = {}
+            annotation_conflicts = set(self.annotations.keys()) & set(other_pattern.annotations.keys())
+            if annotation_conflicts:
+                raise PatternError(f'Annotation keys overlap: {annotation_conflicts}')
+            self.annotations.update(other_pattern.annotations)
 
         port_conflicts = set(self.ports.keys()) & set(other_pattern.ports.keys())
         if port_conflicts:
@@ -415,7 +418,7 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
         elif default_keep:
             pat.refs = copy.copy(self.refs)
 
-        if annotations is not None:
+        if annotations is not None and self.annotations is not None:
             pat.annotations = {k: v for k, v in self.annotations.items() if annotations(k, v)}
         elif default_keep:
             pat.annotations = copy.copy(self.annotations)
diff --git a/masque/utils/types.py b/masque/utils/types.py
index 4060ac4..c06b7b4 100644
--- a/masque/utils/types.py
+++ b/masque/utils/types.py
@@ -5,7 +5,7 @@ from typing import Protocol
 
 
 layer_t = int | tuple[int, int] | str
-annotations_t = dict[str, list[int | float | str]]
+annotations_t = dict[str, list[int | float | str]] | None
 
 
 class SupportsBool(Protocol):