diff --git a/openmc/surface.py b/openmc/surface.py
index 66376c2a0c..afa426fa3b 100644
--- a/openmc/surface.py
+++ b/openmc/surface.py
@@ -988,6 +988,9 @@ class Halfspace(Region):
         self.surface = surface
         self.side = side
 
+    def __invert__(self):
+        return -self.surface if self.side == '+' else +self.surface
+
     @property
     def surface(self):
         return self._surface