diff --git a/src/colvar/PCARMSD.cpp b/src/colvar/PCARMSD.cpp
index dc48aa4116a2b52437551af6fbcbb01b79b5d42d..3e1688e90fa908a3bdd2232e3d1dd4357ecbe83c 100644
--- a/src/colvar/PCARMSD.cpp
+++ b/src/colvar/PCARMSD.cpp
@@ -131,10 +131,9 @@ PLUMED_COLVAR_INIT(ao),squared(true)
 	 // check the units for reading this file: how can they make sense? 
          do_read=mypdb.readFromFilepointer(fp,plumed.getAtoms().usingNaturalUnits(),0.1/atoms.getUnits().getLength());
          if(do_read){
-            unsigned nat=0;
             neigenvects++;
             if(mypdb.getAtomNumbers().size()==0) error("number of atoms in a frame should be more than zero");
-            if(nat==0) nat=mypdb.getAtomNumbers().size();
+            unsigned nat=mypdb.getAtomNumbers().size();
             if(nat!=mypdb.getAtomNumbers().size()) error("frames should have the same number of atoms");
             if(aaa.empty()) aaa=mypdb.getAtomNumbers();
             if(aaa!=mypdb.getAtomNumbers()) error("frames should contain same atoms in same order");
diff --git a/src/core/ActionAtomistic.cpp b/src/core/ActionAtomistic.cpp
index ee64fd7496a383c299c124ffadde97bba2fbe88e..f1012a26f64c6bea8dcbe8e63ba3fc7888b0ed71 100644
--- a/src/core/ActionAtomistic.cpp
+++ b/src/core/ActionAtomistic.cpp
@@ -136,7 +136,7 @@ void ActionAtomistic::calculateAtomicNumericalDerivatives( ActionWithValue* a, c
   for(int j=0;j<nval;j++){
     Value* v=a->copyOutput(j);
     double ref=v->get();
-    if(v->hasDerivatives()>0){
+    if(v->hasDerivatives()){
       for(int i=0;i<natoms;i++) for(int k=0;k<3;k++) {
         double d=(value[j*natoms+i][k]-ref)/delta;
         v->addDerivative(startnum+3*i+k,d);
diff --git a/src/reference/PointWiseMapping.h b/src/reference/PointWiseMapping.h
index 878acc54c6ff0ab45b30e5c2588f8364fcfd99aa..1345e62fc475ca5080da03e6a7129cb940a8fc83 100644
--- a/src/reference/PointWiseMapping.h
+++ b/src/reference/PointWiseMapping.h
@@ -87,7 +87,7 @@ bool PointWiseMapping::mappingNeedsSetup() const {
 
 inline
 void PointWiseMapping::copyFrameDerivatives( const unsigned& from, const unsigned& to ){
-  plumed_dbg_assert( to>=frames.size()/2 & from<frames.size()/2 );
+  plumed_dbg_assert( to>=frames.size()/2 && from<frames.size()/2 );
   frames[to]->copyDerivatives( frames[from] );
 }