diff --git a/src/G4TRandom.hh b/src/G4TRandom.hh
index 90b2cfa..15e551e 100644
--- a/src/G4TRandom.hh
+++ b/src/G4TRandom.hh
@@ -14,6 +14,7 @@
 
 #include <TRandom.h>
 #include <Randomize.hh>
+#include <G4Version.hh>
 
 class G4TRandom : public TRandom {
  public:
@@ -27,7 +28,11 @@ class G4TRandom : public TRandom {
    virtual  UInt_t   GetSeed() const;
    virtual  UInt_t   Integer(UInt_t imax);
    virtual  Double_t Landau(Double_t mean=0, Double_t sigma=1);
+#if G4VERSION_NUMBER >= 1070
    virtual  ULong64_t Poisson(Double_t mean);
+#else
+   virtual  Int_t    Poisson(Double_t mean);
+#endif
    virtual  Double_t PoissonD(Double_t mean);
    virtual  void     Rannor(Float_t &a, Float_t &b);
    virtual  void     Rannor(Double_t &a, Double_t &b);
@@ -79,7 +84,11 @@ inline Double_t G4TRandom::Landau(Double_t mean, Double_t sigma) {
    return CLHEP::RandLandau::shoot() * sigma + mean;
 }
 
+#if G4VERSION_NUMBER >= 1070
 inline ULong64_t G4TRandom::Poisson(Double_t mean) {
+#else
+inline Int_t G4TRandom::Poisson(Double_t mean) {
+#endif
    return CLHEP::RandPoisson::shoot(mean);
 }