diff --git a/pykat/components.py b/pykat/components.py
index 07ecaa376ac62df5c22be95274960e7b743230e4..cc7488d3c47f1a2902545fa040e683f54e619a09 100644
--- a/pykat/components.py
+++ b/pykat/components.py
@@ -339,6 +339,10 @@ class AbstractMirrorComponent(Component):
         if R is not None: self.R.value = R
         if T is not None: self.T.value = T
         if L is not None: self.L.value = L
+        
+        # check energy conservation
+        if self.R.value + self.T.value + self.L.value != 1:
+            raise pkex.BasePyKatException("The specified R, T and L values (%f, %f and %f) violate energy conservation" % (self.R.value, self.T.value, self.L.value))
     
     @property
     def z(self): return self.__z