diff --git a/patches/libecl_dualporo_actnum.patch b/patches/libecl_dualporo_actnum.patch
new file mode 100644
index 0000000000..2c9a1e56ff
--- /dev/null
+++ b/patches/libecl_dualporo_actnum.patch
@@ -0,0 +1,34 @@
+From 978139b8cd9361fa1a5884079e66999ee39ea1bd Mon Sep 17 00:00:00 2001
+From: Magne Sjaastad <magne.sjaastad@ceetronsolutions.com>
+Date: Fri, 31 May 2019 14:37:50 +0200
+Subject: [PATCH] helper function for libecl dual porosity
+
+---
+ ThirdParty/Ert/lib/ecl/ecl_kw_functions.cpp | 9 ++++++++-
+ 1 file changed, 8 insertions(+), 1 deletion(-)
+
+diff --git a/ThirdParty/Ert/lib/ecl/ecl_kw_functions.cpp b/ThirdParty/Ert/lib/ecl/ecl_kw_functions.cpp
+index d10646fd3..e5d980fb1 100644
+--- a/ThirdParty/Ert/lib/ecl/ecl_kw_functions.cpp
++++ b/ThirdParty/Ert/lib/ecl/ecl_kw_functions.cpp
+@@ -143,9 +143,16 @@ ecl_kw_type * ecl_kw_alloc_actnum(const ecl_kw_type * porv_kw, float porv_limit)
+   const float * porv_values = ecl_kw_get_float_ptr(porv_kw);
+   int * actnum_values = ecl_kw_get_int_ptr( actnum_kw);
+ 
++  // When PORV is used as criteria, make sure all active cells are assigned both
++  // active matrix and active fracture. This will make sure that both single porosity
++  // models and dual porosity models in initialized with the correct bit mask
++  // See documentation in top of ecl_grid.cpp
++  //
++  const int combinedActnumValueForMatrixAndFracture = CELL_ACTIVE_MATRIX + CELL_ACTIVE_FRACTURE;
++
+   for (int i=0; i < size; i++) {
+     if (porv_values[i] > porv_limit)
+-      actnum_values[i] = 1;
++      actnum_values[i] = combinedActnumValueForMatrixAndFracture;
+     else
+       actnum_values[i] = 0;
+   }
+-- 
+2.21.0.windows.1
+