diff --git a/SimPEG/Utils/__init__.py b/SimPEG/Utils/__init__.py
index 269cfdc5..1331cc8c 100644
--- a/SimPEG/Utils/__init__.py
+++ b/SimPEG/Utils/__init__.py
@@ -1,5 +1,5 @@
 from matutils import getSubArray, mkvc, ndgrid, ind2sub, sub2ind
-from sputils import spzeros, kron3, speye, sdiag, ddx, av, avExtrap
+from sputils import spzeros, kron3, speye, sdiag, sdInv, ddx, av, avExtrap
 from meshutils import exampleLomGird, meshTensors
 from lomutils import volTetra, faceInfo, inv2X2BlockDiagonal, inv3X3BlockDiagonal, indexCube
 from interputils import interpmat
diff --git a/SimPEG/Utils/sputils.py b/SimPEG/Utils/sputils.py
index 06eef80d..f671be43 100644
--- a/SimPEG/Utils/sputils.py
+++ b/SimPEG/Utils/sputils.py
@@ -7,6 +7,9 @@ def sdiag(h):
     """Sparse diagonal matrix"""
     return sp.spdiags(mkvc(h), 0, h.size, h.size, format="csr")
 
+def sdInv(M):
+    "Inverse of a sparse diagonal matrix"
+    return sdiag(1/M.diagonal())
 
 def speye(n):
     """Sparse identity"""