diff --git a/rocketpy/mathutils/function.py b/rocketpy/mathutils/function.py
index 3d525a0ad..9fd88a5db 100644
--- a/rocketpy/mathutils/function.py
+++ b/rocketpy/mathutils/function.py
@@ -2648,7 +2648,7 @@ def find_input(self, val, start, tol=1e-4):
             The value of the input which gives the output closest to val.
         """
         return optimize.root(
-            lambda x: self.get_value(x) - val,
+            lambda x: self.get_value(x)[0] - val,
             start,
             tol=tol,
         ).x[0]