diff --git a/PhysicsTools/NanoAOD/python/genparticles_cff.py b/PhysicsTools/NanoAOD/python/genparticles_cff.py
index 086ca196288fb..552912c12b230 100644
--- a/PhysicsTools/NanoAOD/python/genparticles_cff.py
+++ b/PhysicsTools/NanoAOD/python/genparticles_cff.py
@@ -41,7 +41,7 @@
          pt  = Var("pt",  float, precision=8),
          phi = Var("phi", float,precision=8),
          eta  = Var("eta",  float,precision=8),
-         mass = Var("?!((abs(pdgId)>=1 && abs(pdgId)<=5) || (abs(pdgId)>=11 && abs(pdgId)<=16) || pdgId==21 || pdgId==111 || abs(pdgId)==211 || abs(pdgId)==421 || abs(pdgId)==411 || (pdgId==22 && mass<1))?mass:0", float,precision="?(abs(pdgId)==6 && statusFlags().isLastCopy())?20:8",doc="Mass stored for all particles with the exception of quarks (except top), leptons/neutrinos, photons with mass < 1 GeV, gluons, pi0(111), pi+(211), D0(421), and D+(411). For these particles, you can lookup the value from PDG."),
+         mass = Var("?!((abs(pdgId)>=1 && abs(pdgId)<=5) || (abs(pdgId)>=11 && abs(pdgId)<=16) || pdgId==21 || pdgId==111 || abs(pdgId)==211 || abs(pdgId)==421 || abs(pdgId)==411 || (pdgId==22 && mass<1))?mass:0", float,precision="?((abs(pdgId)==6 || abs(pdgId)>1000000) && statusFlags().isLastCopy())?20:8",doc="Mass stored for all particles with the exception of quarks (except top), leptons/neutrinos, photons with mass < 1 GeV, gluons, pi0(111), pi+(211), D0(421), and D+(411). For these particles, you can lookup the value from PDG."),
          pdgId  = Var("pdgId", int, doc="PDG id"),
          status  = Var("status", int, doc="Particle status. 1=stable"),
          genPartIdxMother = Var("?numberOfMothers>0?motherRef(0).key():-1", int, doc="index of the mother particle"),
diff --git a/PhysicsTools/NanoAOD/python/nanogen_cff.py b/PhysicsTools/NanoAOD/python/nanogen_cff.py
index 92cba74a9478c..bcbb2431faa13 100644
--- a/PhysicsTools/NanoAOD/python/nanogen_cff.py
+++ b/PhysicsTools/NanoAOD/python/nanogen_cff.py
@@ -55,6 +55,7 @@ def nanoGenCommonCustomize(process):
     setGenPtPrecision(process, CandVars.pt.precision)
     setGenEtaPrecision(process, CandVars.eta.precision)
     setGenPhiPrecision(process, CandVars.phi.precision)
+    setGenMassPrecision(process, CandVars.mass.precision)
 
 def customizeNanoGENFromMini(process):
     process.nanogenSequence.insert(0, process.genParticles2HepMCHiggsVtx)
@@ -126,9 +127,11 @@ def pruneGenParticlesMini(process):
     return process
 
 def setGenFullPrecision(process):
-    setGenPtPrecision(process, 23)
-    setGenEtaPrecision(process, 23)
-    setGenPhiPrecision(process, 23)
+    process = setGenPtPrecision(process, 23)
+    process = setGenEtaPrecision(process, 23)
+    process = setGenPhiPrecision(process, 23)
+    process = setGenMassPrecision(process, 23)
+    return process
 
 def setGenPtPrecision(process, precision):
     process.genParticleTable.variables.pt.precision = precision
@@ -147,6 +150,11 @@ def setGenPhiPrecision(process, precision):
     process.metMCTable.variables.phi.precision = precision
     return process
 
+def setGenMassPrecision(process, precision):
+    process.genParticleTable.variables.mass.precision = precision
+    process.genJetTable.variables.mass.precision = precision
+    return process
+
 def setLHEFullPrecision(process):
     process.lheInfoTable.precision = 23
     return process