diff --git a/masque/repetition.py b/masque/repetition.py
index cc30d20..9742733 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -98,7 +98,7 @@ class GridRepetition:
 
         if val.size != 2:
             raise PatternError('Offset must be convertible to size-2 ndarray')
-        self._offset = val.flatten()
+        self._offset = val.flatten().astype(float)
 
     # dose property
     @property
diff --git a/masque/subpattern.py b/masque/subpattern.py
index 811c670..0415894 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -57,7 +57,7 @@ class SubPattern:
 
         if val.size != 2:
             raise PatternError('Offset must be convertible to size-2 ndarray')
-        self._offset = val.flatten()
+        self._offset = val.flatten().astype(float)
 
     # dose property
     @property