diff --git a/src/KSPACE/pppm.h b/src/KSPACE/pppm.h
index a7d0dfb2cd..6c3e697ecf 100644
--- a/src/KSPACE/pppm.h
+++ b/src/KSPACE/pppm.h
@@ -122,8 +122,8 @@ class PPPM : public KSpace {
   double estimate_ik_error(double, double, bigint);
   double compute_qopt();
   void compute_gf_denom();
-  void compute_gf_ik();
-  void compute_gf_ad();
+  virtual void compute_gf_ik();
+  virtual void compute_gf_ad();
   void compute_sf_precoeff();
   
   virtual void particle_map();
@@ -131,12 +131,12 @@ class PPPM : public KSpace {
   virtual void brick2fft();
   
   virtual void poisson();
-  void poisson_ik();
-  void poisson_ad();
+  virtual void poisson_ik();
+  virtual void poisson_ad();
   
   virtual void fieldforce();
-  void fieldforce_ik();
-  void fieldforce_ad();
+  virtual void fieldforce_ik();
+  virtual void fieldforce_ad();
   
   virtual void poisson_peratom();
   virtual void fieldforce_peratom();
diff --git a/src/KSPACE/pppm_tip4p.cpp b/src/KSPACE/pppm_tip4p.cpp
index d6c1ddaf0c..4abd241006 100644
--- a/src/KSPACE/pppm_tip4p.cpp
+++ b/src/KSPACE/pppm_tip4p.cpp
@@ -162,16 +162,6 @@ void PPPMTIP4P::make_rho()
   }
 }
 
-/* ----------------------------------------------------------------------
-   interpolate from grid to get electric field & force on my particles
-------------------------------------------------------------------------- */
-
-void PPPMTIP4P::fieldforce()
-{
-  if (differentiation_flag == 1) fieldforce_ad();
-  else fieldforce_ik();
-}
-
 /* ----------------------------------------------------------------------
    interpolate from grid to get electric field & force on my particles for ik
 ------------------------------------------------------------------------- */
diff --git a/src/KSPACE/pppm_tip4p.h b/src/KSPACE/pppm_tip4p.h
index 6726af2ad6..a6d4a51cfe 100644
--- a/src/KSPACE/pppm_tip4p.h
+++ b/src/KSPACE/pppm_tip4p.h
@@ -33,9 +33,8 @@ class PPPMTIP4P : public PPPM {
  protected:
   virtual void particle_map();
   virtual void make_rho();
-  virtual void fieldforce();
-  void fieldforce_ik();
-  void fieldforce_ad();
+  virtual void fieldforce_ik();
+  virtual void fieldforce_ad();
   virtual void fieldforce_peratom();
 
  private: