diff --git a/SimPEG/Maps.py b/SimPEG/Maps.py
index be789a2a..a7f5a0ab 100644
--- a/SimPEG/Maps.py
+++ b/SimPEG/Maps.py
@@ -19,7 +19,7 @@ class IdentityMap(object):
         Utils.setKwargs(self, **kwargs)
 
         if nP is not None:
-            assert type(nP) in [int, long], ' Number of parameters must be an integer.'
+            assert type(nP) in [int, long, np.int64], ' Number of parameters must be an integer.'
 
         self.mesh = mesh
         self._nP  = nP
@@ -1492,7 +1492,7 @@ class ParametrizedBlockInLayer(IdentityMap):
         self._validate_m(m) # make sure things are the right sizes
 
         if self.mesh.dim == 2:
-            return self._deriv2d(m)
+            return sp.csr_matrix(self._deriv2d(m))
         elif self.mesh.dim == 3:
-            return self._deriv3d(m)
+            return sp.csr_matrix(self._deriv3d(m))
 
diff --git a/SimPEG/Regularization.py b/SimPEG/Regularization.py
index fc101a61..d4de1705 100644
--- a/SimPEG/Regularization.py
+++ b/SimPEG/Regularization.py
@@ -39,7 +39,7 @@ class RegularizationMesh(object):
             if self.indActive is None:
                 self._nC = self.mesh.nC
             else:
-                self._nC = sum(self.indActive)
+                self._nC = int(sum(self.indActive))
         return self._nC
 
     @property
@@ -304,7 +304,7 @@ class BaseRegularization(object):
     mesh    = None    #: A SimPEG.Mesh instance.
     mref    = None    #: Reference model.
 
-    def __init__(self, mesh, mapping=None, indActive=None, **kwargs):
+    def __init__(self, mesh=None, nP=None, mapping=None, indActive=None, **kwargs):
         Utils.setKwargs(self, **kwargs)
         assert isinstance(mesh, Mesh.BaseMesh), "mesh must be a SimPEG.Mesh object."
         if indActive is not None and indActive.dtype != 'bool':
@@ -314,11 +314,19 @@ class BaseRegularization(object):
         if indActive is not None and mapping is None:
             mapping = Maps.IdentityMap(nP=indActive.nonzero()[0].size)
 
+        if mesh is None and nP is None:
+            raise Exception, 'either Mesh or number of parameters must be provided to the BaseRegularization'
+
         self.regmesh = RegularizationMesh(mesh,indActive)
-        self.mapping = mapping or self.mapPair(mesh)
-        self.mapping._assertMatchesPair(self.mapPair)
         self.indActive = indActive
 
+        if mesh is not None and nP is None:
+            nP = self.regmesh.nC
+        self.nP = nP
+
+        self.mapping = mapping or self.mapPair(nP=self.nP)
+        self.mapping._assertMatchesPair(self.mapPair)
+
     @property
     def parent(self):
         """This is the parent of the regularization."""
@@ -346,7 +354,7 @@ class BaseRegularization(object):
     @property
     def W(self):
         """Full regularization weighting matrix W."""
-        return sp.identity(self.regmesh.nC)
+        return sp.identity(self.nP)
 
     @Utils.timeIt
     def eval(self, m):