diff --git a/pdpasmhelper.py b/pdpasmhelper.py
index 7e77e37..6b58343 100644
--- a/pdpasmhelper.py
+++ b/pdpasmhelper.py
@@ -182,6 +182,9 @@ class PDP11InstructionAssembler:
     def inc(self, dst):
         return self._1op(0o005200, dst)
 
+    def dec(self, dst):
+        return self._1op(0o005300, dst)
+
     def halt(self):
         return self.literal(0)