diff --git a/src/cltools/Driver.cpp b/src/cltools/Driver.cpp
index b826c3b1fc..1becea88a5 100644
--- a/src/cltools/Driver.cpp
+++ b/src/cltools/Driver.cpp
@@ -727,7 +727,9 @@ int Driver<real>::main(FILE* in,FILE*out,Communicator& pc) {
         std::map<std::string,std::vector<std::string> > data;
         IFile ifile; ifile.open(plumedFile); std::vector<std::string> words;
         while( Tools::getParsedLine(ifile,words) && !p.getEndPlumed() ) {
-          p.readInputWords(words,false); Action* aa=p.getActionSet()[p.getActionSet().size()-1].get();
+          p.readInputWords(words,false);
+          Action* aa=p.getActionSet()[p.getActionSet().size()-1].get();
+          plumed_assert(aa); // needed for following calls, see #1046
           ActionWithValue* av=aa->castToActionWithValue();
           if( av && aa->getDefaultString().length()>0 ) {
             std::vector<std::string> def; def.push_back( "defaults " + aa->getDefaultString() );
diff --git a/src/core/ActionAtomistic.cpp b/src/core/ActionAtomistic.cpp
index f4d268bb94..c0de85bd7c 100644
--- a/src/core/ActionAtomistic.cpp
+++ b/src/core/ActionAtomistic.cpp
@@ -53,6 +53,7 @@ ActionAtomistic::ActionAtomistic(const ActionOptions&ao):
   // We now get all the information about atoms that are lying about
   std::vector<ActionWithValue*> vatoms = plumed.getActionSet().select<ActionWithValue*>();
   for(const auto & vv : vatoms ) {
+    plumed_assert(vv); // needed for following calls, see #1046
     ActionToPutData* ap = vv->castToActionToPutData();
     if( ap ) {
       if( ap->getRole()=="x" ) xpos.push_back( ap->copyOutput(0) );
@@ -324,11 +325,15 @@ std::pair<std::size_t, std::size_t> ActionAtomistic::getValueIndices( const Atom
 
 void ActionAtomistic::retrieveAtoms( const bool& force ) {
   if( boxValue ) {
-    PbcAction* pbca = boxValue->getPntrToAction()->castToPbcAction();
+    auto* ptr=boxValue->getPntrToAction();
+    plumed_assert(ptr); // needed for following calls, see #1046
+    PbcAction* pbca = ptr->castToPbcAction();
     plumed_assert( pbca ); pbc=pbca->pbc;
   }
   if( donotretrieve || indexes.size()==0 ) return;
-  ActionToPutData* cv = chargev[0]->getPntrToAction()->castToActionToPutData();
+  auto * ptr=chargev[0]->getPntrToAction();
+  plumed_assert(ptr); // needed for following calls, see #1046
+  ActionToPutData* cv = ptr->castToActionToPutData();
   if(cv) chargesWereSet=cv->hasBeenSet();
   unsigned j = 0;
 
diff --git a/src/core/ActionToPutData.cpp b/src/core/ActionToPutData.cpp
index 06988487f0..ad9648b734 100644
--- a/src/core/ActionToPutData.cpp
+++ b/src/core/ActionToPutData.cpp
@@ -160,7 +160,9 @@ void ActionToPutData::apply() {
 
 unsigned ActionToPutData::getNumberOfForcesToRescale() const {
   if( getName()!="ENERGY" || getDependencies().size()>0 ) return copyOutput(0)->getNumberOfValues();
-  plumed_assert( getDependencies().size()==1 ); ActionForInterface* ai = getDependencies()[0]->castToActionForInterface();
+  plumed_assert( getDependencies().size()==1 );
+  plumed_assert(getDependencies()[0]); // needed for following calls, see #1046
+  ActionForInterface* ai = getDependencies()[0]->castToActionForInterface();
   return ai->getNumberOfForcesToRescale();
 }
 
diff --git a/src/core/ActionWithArguments.cpp b/src/core/ActionWithArguments.cpp
index d35f7f9047..8e84498f9a 100644
--- a/src/core/ActionWithArguments.cpp
+++ b/src/core/ActionWithArguments.cpp
@@ -107,6 +107,7 @@ void ActionWithArguments::interpretArgumentList(const std::vector<std::string>&
           std::vector<ActionWithValue*> all=as.select<ActionWithValue*>();
           if( all.empty() ) readact->error("your input file is not telling plumed to calculate anything");
           for(unsigned j=0; j<all.size(); j++) {
+            plumed_assert(all[j]); // needed for following calls, see #1046
             ActionForInterface* ap=all[j]->castToActionForInterface(); if( ap ) continue;
             for(int k=0; k<all[j]->getNumberOfComponents(); ++k) arg.push_back(all[j]->copyOutput(k));
           }
@@ -166,6 +167,7 @@ void ActionWithArguments::interpretArgumentList(const std::vector<std::string>&
           std::vector<ActionWithValue*> all=as.select<ActionWithValue*>();
           if( all.empty() ) readact->error("your input file is not telling plumed to calculate anything");
           for(unsigned j=0; j<all.size(); j++) {
+            plumed_assert(all[j]); // needed for following calls, see #1046
             ActionWithVirtualAtom* av=all[j]->castToActionWithVirtualAtom(); if( av ) continue;
             ActionForInterface* ap=all[j]->castToActionForInterface(); if( ap && all[j]->getName()!="ENERGY" ) continue;
             for(int k=0; k<all[j]->getNumberOfComponents(); ++k) arg.push_back(all[j]->copyOutput(k));
@@ -327,7 +329,9 @@ bool ActionWithArguments::calculateConstantValues( const bool& haveatoms ) {
   if( !av || arguments.size()==0 ) return false;
   bool constant = true, atoms=false;
   for(unsigned i=0; i<arguments.size(); ++i) {
-    ActionAtomistic* aa=arguments[i]->getPntrToAction()->castToActionAtomistic();
+    auto * ptr=arguments[i]->getPntrToAction();
+    plumed_assert(ptr); // needed for following calls, see #1046
+    ActionAtomistic* aa=ptr->castToActionAtomistic();
     if( aa ) {
       ActionWithVector* av=dynamic_cast<ActionWithVector*>( arguments[i]->getPntrToAction() );
       if( !av || aa->getNumberOfAtoms()>0 ) atoms=true;
diff --git a/src/core/PlumedMain.cpp b/src/core/PlumedMain.cpp
index c7c87540fc..63a78c2189 100644
--- a/src/core/PlumedMain.cpp
+++ b/src/core/PlumedMain.cpp
@@ -434,6 +434,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
         CHECK_INIT(initialized,word);
         CHECK_NOTNULL(val,word);
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) dd->setAtomsNlocal(val.get<int>());
         }
@@ -441,6 +442,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
       case cmd_setAtomsGatindex:
         CHECK_INIT(initialized,word);
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) dd->setAtomsGatindex(val,false);
         }
@@ -448,6 +450,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
       case cmd_setAtomsFGatindex:
         CHECK_INIT(initialized,word);
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) dd->setAtomsGatindex(val,false);
         }
@@ -456,6 +459,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
         CHECK_INIT(initialized,word);
         CHECK_NOTNULL(val,word);
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) dd->setAtomsContiguous(val.get<int>());
         }
@@ -464,6 +468,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
         CHECK_INIT(initialized,word);
         CHECK_NOTNULL(val,word);
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) dd->createFullList(val);
         }
@@ -474,6 +479,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
         CHECK_NOTNULL(val,word);
         unsigned nlists=0;
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) { dd->getFullList(val); nlists++; }
         }
@@ -483,6 +489,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
       case cmd_clearFullList:
         CHECK_INIT(initialized,word);
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if( dd ) dd->clearFullList();
         }
@@ -540,6 +547,7 @@ void PlumedMain::cmd(std::string_view word,const TypesafePtr & val) {
         CHECK_INIT(initialized,word);
         std::vector<int> natoms;
         for(const auto & pp : inputs ) {
+          plumed_assert(pp);
           DomainDecomposition* dd=pp->castToDomainDecomposition();
           if ( dd ) natoms.push_back( dd->getNumberOfAtoms() );
         }
@@ -873,6 +881,7 @@ void PlumedMain::init() {
   log<<"Number of threads: "<<OpenMP::getNumThreads()<<"\n";
   log<<"Cache line size: "<<OpenMP::getCachelineSize()<<"\n";
   for(const auto & pp : inputs ) {
+    plumed_assert(pp);
     DomainDecomposition* dd=pp->castToDomainDecomposition();
     if ( dd ) log.printf("Number of atoms: %d\n",dd->getNumberOfAtoms());
   }
@@ -1123,6 +1132,7 @@ void PlumedMain::justCalculate() {
 // calculate the active actions in order (assuming *backward* dependence)
   for(const auto & pp : actionSet) {
     Action* p(pp.get());
+    plumed_assert(p);
     try {
       if(p->isActive()) {
 // Stopwatch is stopped when sw goes out of scope.