diff --git a/vm/nga-python/Memory.py b/vm/nga-python/Memory.py
index 9150a35..357fb81 100644
--- a/vm/nga-python/Memory.py
+++ b/vm/nga-python/Memory.py
@@ -11,9 +11,13 @@ class Memory():
             self.memory[i] = cell
             i = i + 1
         f.close()
+        self.length = size
     
     def store(self, value, address):
         self.memory[address] = value
     
     def fetch(self, address):
         return self.memory[address]
+    
+    def size(self):
+        return self.length
diff --git a/vm/nga-python/retro.py b/vm/nga-python/retro.py
index 2e32f78..7946f0b 100644
--- a/vm/nga-python/retro.py
+++ b/vm/nga-python/retro.py
@@ -258,7 +258,7 @@ def i_fe():
     elif target == -2:
         stack.push(len(address))
     elif target == -3:
-        stack.push(len(memory))
+        stack.push(memory.size())
     elif target == -4:
         stack.push(2147483648)
     elif target == -5:
@@ -647,4 +647,3 @@ if __name__ == "__main__":
     else:
         for source in sources:
             run_file(source)
-