diff --git a/bfps/NavierStokes.py b/bfps/NavierStokes.py
index 8f2d22ef28f227470b7d62e9efae00500e2d8577..a0edce331da01b172efba8b2530251ceb0b770b0 100644
--- a/bfps/NavierStokes.py
+++ b/bfps/NavierStokes.py
@@ -350,6 +350,7 @@ class NavierStokes(bfps.fluid_base.fluid_particle_base):
             neighbours = 1,
             smoothness = 1,
             name = 'particle_field'):
+        self.fluid_includes += '#include "interpolator.hpp"\n'
         self.fluid_variables += 'interpolator<{0}, {1}> *vel_{2}, *acc_{2};\n'.format(self.C_dtype, neighbours, name)
         self.parameters[name + '_type'] = interp_type
         self.parameters[name + '_neighbours'] = neighbours