diff --git a/mapytex/calculus/core/MO/exceptions.py b/mapytex/calculus/core/MO/exceptions.py
index a9b7c1e..ec498d4 100644
--- a/mapytex/calculus/core/MO/exceptions.py
+++ b/mapytex/calculus/core/MO/exceptions.py
@@ -10,6 +10,9 @@
 Exceptions for core tools
 """
 
+class MOError(Exception):
+    pass
+
 
 # -----------------------------
 # Reglages pour 'vim'
diff --git a/mapytex/calculus/core/MO/mo.py b/mapytex/calculus/core/MO/mo.py
index b1a28b8..b3637f3 100644
--- a/mapytex/calculus/core/MO/mo.py
+++ b/mapytex/calculus/core/MO/mo.py
@@ -7,15 +7,13 @@
 # Distributed under terms of the MIT license.
 
 from decimal import Decimal
+from .exceptions import MOError
 from ..coroutine import coroutine, STOOOP
 from ..renders import tree2txt, tree2tex
 
 
 __all__ = ["moify", "MO", "MOstr"]
 
-class MOError(Exception):
-    pass
-
 @coroutine
 def moify(target):
     """ Coroutine which try to convert everything into an MO """
@@ -125,7 +123,7 @@ class MOnumber(MO):
         >>> MOnumber("a")
         Traceback (most recent call last):
             ...
-        mapytex.calculus.core.MO.mo.MOError: The value of an MOnumber need to be a int, a float or a Decimal
+        mapytex.calculus.core.MO.exceptions.MOError: The value of an MOnumber need to be a int, a float or a Decimal
 
         """
         try:
@@ -293,15 +291,15 @@ class MOstr(MO):
         >>> a = MOstr("+")
         Traceback (most recent call last):
             ...
-        mapytex.calculus.core.MO.mo.MOError: An MOstr should be initiate with a alpha string, got +
+        mapytex.calculus.core.MO.exceptions.MOError: An MOstr should be initiate with a alpha string, got +
         >>> MOstr("ui")
         Traceback (most recent call last):
             ...
-        mapytex.calculus.core.MO.mo.MOError: An MOstr should be initiate with a single caracter string, got ui
+        mapytex.calculus.core.MO.exceptions.MOError: An MOstr should be initiate with a single caracter string, got ui
         >>> MOstr(2)
         Traceback (most recent call last):
             ...
-        mapytex.calculus.core.MO.mo.MOError: An MOstr should be initiate with a string - the unknown, got 2
+        mapytex.calculus.core.MO.exceptions.MOError: An MOstr should be initiate with a string - the unknown, got 2
 
         """
         try: