diff --git a/src/main.cpp b/src/main.cpp
index 3921eee..caad6f2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -115,7 +115,7 @@ int main(int argc, char* argv[]) {
         // entry loop
         while (go_on) {
             // make program from interactive entry
-            program prog(&_global_stack, &_global_heap);
+            program prog(&_global_stack, _global_heap);
             switch (program::entry(prog)) {
                 case ret_good_bye:
                     go_on = false;
@@ -140,7 +140,7 @@ int main(int argc, char* argv[]) {
     }
     // run with cmd line arguments
     else {
-        program prog(&_global_stack, &_global_heap);
+        program prog(&_global_stack, _global_heap);
         string entry;
         int i;
 
diff --git a/src/program.hpp b/src/program.hpp
index b89c9ec..8351c6e 100644
--- a/src/program.hpp
+++ b/src/program.hpp
@@ -44,7 +44,7 @@ struct if_layout_t {
 //< program class: the class containing a string parser, all the programs keywords, a stack for running the program
 class program : public deque<object*> {
    public:
-    program(rpnstack* stk, heap* hp, program* parent = nullptr):_stack(stk),_heap(hp),_parent(parent) {
+    program(rpnstack* stk, heap& hp, program* parent = nullptr):_stack(stk),_heap(hp),_parent(parent) {
         interrupt_now = false;
     }
     virtual ~program() {
@@ -85,7 +85,7 @@ class program : public deque<object*> {
     rpnstack* _stack;
 
     // global heap (sto, rcl)
-    heap* _heap;
+    heap& _heap;
 
     // local heap for local loop variables (for..next)
     heap _local_heap;
diff --git a/src/rpn-program.cpp b/src/rpn-program.cpp
index abe92ae..3efb4d8 100644
--- a/src/rpn-program.cpp
+++ b/src/rpn-program.cpp
@@ -22,7 +22,7 @@ bool program::find_variable(string& variable, object*& obj) {
             parent = parent->_parent;
         }
         if (!found) {
-            if (_heap->get(variable, obj)) found = true;
+            if (_heap.get(variable, obj)) found = true;
         }
     }
 
diff --git a/src/rpn-store.cpp b/src/rpn-store.cpp
index 7f6e037..09c9a26 100644
--- a/src/rpn-store.cpp
+++ b/src/rpn-store.cpp
@@ -7,12 +7,12 @@ void program::rpn_sto(void) {
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
 
     // store symbol with first value
-    const auto it = _heap->find(_stack->value<ostring>(0));
-    if (it != _heap->end()) {
+    const auto it = _heap.find(_stack->value<ostring>(0));
+    if (it != _heap.end()) {
         delete it->second;
-        _heap->erase(it);
+        _heap.erase(it);
     }
-    (*_heap)[_stack->value<ostring>(0)] = _stack->at(1)->clone();
+    _heap[_stack->value<ostring>(0)] = _stack->at(1)->clone();
     _stack->pop_front(2);
 }
 
@@ -21,7 +21,7 @@ void program::rpn_sto(void) {
 void program::rpn_stoadd(void) {
     MIN_ARGUMENTS(2);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
-    if (_heap->find(_stack->value<ostring>(0)) == _heap->end()) {
+    if (_heap.find(_stack->value<ostring>(0)) == _heap.end()) {
         ERR_CONTEXT(ret_unknown_variable);
         return;
     }
@@ -38,7 +38,7 @@ void program::rpn_stoadd(void) {
 void program::rpn_stosub(void) {
     MIN_ARGUMENTS(2);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
-    if (_heap->find(_stack->value<ostring>(0)) == _heap->end()) {
+    if (_heap.find(_stack->value<ostring>(0)) == _heap.end()) {
         ERR_CONTEXT(ret_unknown_variable);
         return;
     }
@@ -55,7 +55,7 @@ void program::rpn_stosub(void) {
 void program::rpn_stomul(void) {
     MIN_ARGUMENTS(2);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
-    if (_heap->find(_stack->value<ostring>(0)) == _heap->end()) {
+    if (_heap.find(_stack->value<ostring>(0)) == _heap.end()) {
         ERR_CONTEXT(ret_unknown_variable);
         return;
     }
@@ -72,7 +72,7 @@ void program::rpn_stomul(void) {
 void program::rpn_stodiv(void) {
     MIN_ARGUMENTS(2);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
-    if (_heap->find(_stack->value<ostring>(0)) == _heap->end()) {
+    if (_heap.find(_stack->value<ostring>(0)) == _heap.end()) {
         ERR_CONTEXT(ret_unknown_variable);
         return;
     }
@@ -89,7 +89,7 @@ void program::rpn_stodiv(void) {
 void program::rpn_stoneg(void) {
     MIN_ARGUMENTS(1);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
-    if (_heap->find(_stack->value<ostring>(0)) == _heap->end()) {
+    if (_heap.find(_stack->value<ostring>(0)) == _heap.end()) {
         ERR_CONTEXT(ret_unknown_variable);
         return;
     }
@@ -105,7 +105,7 @@ void program::rpn_stoneg(void) {
 void program::rpn_stoinv(void) {
     MIN_ARGUMENTS(1);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
-    if (_heap->find(_stack->value<ostring>(0)) == _heap->end()) {
+    if (_heap.find(_stack->value<ostring>(0)) == _heap.end()) {
         ERR_CONTEXT(ret_unknown_variable);
         return;
     }
@@ -174,10 +174,10 @@ void program::rpn_purge(void) {
     MIN_ARGUMENTS(1);
     ARG_MUST_BE_OF_TYPE(0, cmd_symbol);
 
-    const auto i = _heap->find(_stack->value<symbol>(0));
-    if (i != _heap->end()) {
+    const auto i = _heap.find(_stack->value<symbol>(0));
+    if (i != _heap.end()) {
         delete i->second;
-        _heap->erase(i);
+        _heap.erase(i);
     } else
         ERR_CONTEXT(ret_unknown_variable);
     _stack->pop();
@@ -191,8 +191,8 @@ void program::rpn_vars(void) {
     string name;
 
     // heap variables
-    for (int i = 0; i < (int)_heap->size(); i++) {
-        (void)_heap->get_by_index(i, name, obj);
+    for (int i = 0; i < (int)_heap.size(); i++) {
+        (void)_heap.get_by_index(i, name, obj);
         cout<<"var "<<i+1<<": name '"<<name<<"', type "<<obj->name()<<", value ";
         obj->show(cout);
         cout<<endl;
@@ -220,4 +220,4 @@ void program::rpn_vars(void) {
 
 /// @brief clusr keyword implementation
 ///
-void program::rpn_clusr(void) { _heap->clear(); }
+void program::rpn_clusr(void) { _heap.clear(); }
diff --git a/src/rpn-test-framework.cpp b/src/rpn-test-framework.cpp
index bbb2572..57fedd9 100644
--- a/src/rpn-test-framework.cpp
+++ b/src/rpn-test-framework.cpp
@@ -227,7 +227,7 @@ void program::test(string test_filename, int& total_tests, int& total_tests_fail
                 // parse entry and run line
                 entry = regex_replace(entry, regex("`"), "");
                 if (!entry.empty()) {
-                    program prog(&stk, &hp);
+                    program prog(&stk, hp);
                     ret = program::parse(entry, prog);
                     if (ret == ret_ok) {
                         // run it