diff --git a/PyCircTools/Exceptions/OperatorsExceptions.py b/PyCircTools/Exceptions/OperatorsExceptions.py
index 5f3e9eb..13732af 100644
--- a/PyCircTools/Exceptions/OperatorsExceptions.py
+++ b/PyCircTools/Exceptions/OperatorsExceptions.py
@@ -41,6 +41,15 @@ def __init__(self, curr_size, req_size):
         super().__init__(self.msg)
 
 
+class WrongRange(OperatorException):
+    """
+    WrongRange is raised when the number of inputs is lower or equal than the number of inputs in certain modules.
+    """
+    def __init(self, obj):
+        self.msg = "Number of inputs of " + obj + " must be lower than the number of outputs."
+        super().__init__(self.msg)
+
+
 def get_adder_type(addr_class):
     """
     Method used to get the type of adder used.
diff --git a/PyCircTools/Operators/Extender.py b/PyCircTools/Operators/Extender.py
index e6297dc..d61900c 100644
--- a/PyCircTools/Operators/Extender.py
+++ b/PyCircTools/Operators/Extender.py
@@ -1,4 +1,4 @@
-from PyCircTools import NotTruthValue, NotControlList, WrongSize
+from PyCircTools import NotTruthValue, NotControlList, WrongSize, WrongRange
 
 
 class Extender:
@@ -18,11 +18,14 @@ def __init__(self, into=2, out=4, pure=True):
         :param pure: Used to know if the input is in pure binary or two's complement.
         :type pure: bool
         """
+        if into >= out:
+            raise WrongRange("Extender")
+
         self.numInto = into
         self.numOut = out
         self.pure = pure
         self.input = [False] * into
-        self.output = self.__calculate_output()
+        self.output = [False] * out
 
     def get_numIn(self):
         """
@@ -96,7 +99,7 @@ def set_input(self, values, pure=True):
 
         self.input = values
         self.__set_pure(pure)
-        self.output == self.__calculate_output()
+        self.__calculate_output()
 
         return self
 
@@ -135,4 +138,5 @@ def __calculate_output(self):
                 else:
                     output.append(self.input[self.numInto - 1])
 
-        return output
+        self.output = output
+        return self
diff --git a/PyCircTools/Operators/__init__.py b/PyCircTools/Operators/__init__.py
index 9e8f4fd..7d98f55 100644
--- a/PyCircTools/Operators/__init__.py
+++ b/PyCircTools/Operators/__init__.py
@@ -8,3 +8,4 @@
 from PyCircTools.Operators.Subtractor import *
 from PyCircTools.Operators.Alu import *
 from PyCircTools.Operators.Shifter import *
+from PyCircTools.Operators.Extender import *
diff --git a/tests/Operators_tests/test_extender.py b/tests/Operators_tests/test_extender.py
new file mode 100644
index 0000000..e3d736b
--- /dev/null
+++ b/tests/Operators_tests/test_extender.py
@@ -0,0 +1,18 @@
+from PyCircTools import Extender
+
+
+def test_extender():
+    ext = Extender()
+
+    assert ext.set_input([True, True]).get_output() == [True, True, False, False]
+    assert ext.get_numIn() == 2
+    assert ext.get_numOut() == 4
+
+    _ext = Extender(4, 8)
+
+    assert _ext.numInto == 4
+    assert _ext.numOut == 8
+    assert _ext.set_input([False, False, True, False]).get_output() == [False, False, True, False, False, False, False,
+                                                                        False]
+    assert _ext.set_input([True, False, True, True], False).get_output() == [True, False, True, True, True, True, True,
+                                                                             True]