diff --git a/mapytex/calculus/core/MO/monomial.py b/mapytex/calculus/core/MO/monomial.py
index 0ecc764..eaaa404 100644
--- a/mapytex/calculus/core/MO/monomial.py
+++ b/mapytex/calculus/core/MO/monomial.py
@@ -101,10 +101,11 @@ class MOMonomial(MO):
             raise MOError("The coefficient of a monomial should not be 0")
         self._coefficient = _coefficient
 
-        if isinstance(variable, MOstrPower):
-            _variable = variable.variable
-            _power = MO.factory(variable.power.value * power)
-        elif isinstance(variable, MOstr):
+        _variable = MO.factory(variable)
+        if isinstance(_variable, MOstrPower):
+            _power = MO.factory(_variable.power.value * power)
+            _variable = _variable.variable
+        elif isinstance(_variable, MOstr):
             _variable = variable
             _power = MO.factory(power)
         else: