diff --git a/nutils/evaluable.py b/nutils/evaluable.py
index 47a7d21be..283a53521 100644
--- a/nutils/evaluable.py
+++ b/nutils/evaluable.py
@@ -1088,7 +1088,7 @@ def __init__(self, lgrad:asarray):
   def evalf(self, lgrad):
     n = lgrad[...,-1]
     if equalindex(n.shape[-1], 1): # geom is 1D
-      return numpy.sign(n)
+      return numpy.sign(n).astype(float)
     # orthonormalize n to G
     G = lgrad[...,:-1]
     GG = numeric.contract(G[...,:,_,:], G[...,:,:,_], axis=-3)