diff --git a/src/main/py/read_math_function.py b/src/main/py/read_math_function.py
index d695a46..6886de1 100644
--- a/src/main/py/read_math_function.py
+++ b/src/main/py/read_math_function.py
@@ -130,4 +130,6 @@ def difference_of_simplified_exponential_functions(type, function):
     new_subtrahend = simplify_exponential_function('e', subtrahend)
     if new_minuend != "Der Ausdruck muss die Variable 'x' enthalten." and new_subtrahend != "Der Ausdruck muss die Variable 'x' enthalten.":
         simplified = new_minuend - new_subtrahend
-        return simplified
\ No newline at end of file
+        return simplified
+    else:
+        return "Der Ausdruck muss die Variable 'x' enthalten."
\ No newline at end of file