diff --git a/src/simulation/m_ibm.fpp b/src/simulation/m_ibm.fpp
index 99aeb1e382..d8bdaa2cc5 100644
--- a/src/simulation/m_ibm.fpp
+++ b/src/simulation/m_ibm.fpp
@@ -1143,7 +1143,7 @@ contains
             patch_ib(ib_idx)%moment = 1._wp
             return
         else
-            normal_axis = axis/sqrt(sum(axis))
+            normal_axis = axis/sqrt(sum(axis**2))
         end if
 
         ! if the IB is in 2D or a 3D sphere, we can compute this exactly