diff --git a/src/classes/PFunction.cpp b/src/classes/PFunction.cpp
index 712988a4..eb821302 100644
--- a/src/classes/PFunction.cpp
+++ b/src/classes/PFunction.cpp
@@ -594,10 +594,9 @@ void PFunction::EvalTreeForString(tree_parse_info<> info)
  *
  * \param i iterator of the AST tree
  */
-void PFunction::EvalTreeForStringExpression(iter_t const& i)
+void PFunction::EvalTreeForStringExpression(iter_t const& i, bool funcFlag)
 {
   static Int_t termOp = 0;
-  static bool funcFlag = false;
 
   if (i->value.id() == PFunctionGrammar::realID) {
     assert(i->children.size() == 0);
@@ -629,21 +628,19 @@ void PFunction::EvalTreeForStringExpression(iter_t const& i)
     fFuncString += boost::algorithm::trim_copy(std::string(i->value.begin(), i->value.end())).c_str();
   } else if (i->value.id() == PFunctionGrammar::functionID) {
     assert(i->children.size() == 3);    
-    funcFlag = true;
     fFuncString += std::string(i->value.begin(), i->value.end()).c_str(); // keep function name
     fFuncString += "(";
     // '(', expression, ')'
-    EvalTreeForStringExpression(i->children.begin()+1); // the real stuff
+    EvalTreeForStringExpression(i->children.begin()+1, true); // the real stuff
     fFuncString += ")";
   } else if (i->value.id() == PFunctionGrammar::powerID) {
     assert(i->children.size() == 5);
-    funcFlag = true;
     fFuncString += std::string(i->value.begin(), i->value.end()).c_str(); // keep function name
     fFuncString += "(";
     // '(', expression, ',' expression, ')'
-    EvalTreeForStringExpression(i->children.begin()+1); // base expression
+    EvalTreeForStringExpression(i->children.begin()+1, true); // base expression
     fFuncString += ",";
-    EvalTreeForStringExpression(i->children.begin()+3); // exponent expression
+    EvalTreeForStringExpression(i->children.begin()+3, true); // exponent expression
     fFuncString += ")";
   } else if (i->value.id() == PFunctionGrammar::factorID) {
     EvalTreeForStringExpression(i->children.begin());
@@ -689,7 +686,6 @@ void PFunction::EvalTreeForStringExpression(iter_t const& i)
     }
     if ((termOp > 0) && !funcFlag)
       fFuncString += ")";
-    funcFlag = false;
   } else if (i->value.id() == PFunctionGrammar::assignmentID) {
     assert(i->children.size() == 3);
     EvalTreeForStringExpression(i->children.begin());
diff --git a/src/include/PFunction.h b/src/include/PFunction.h
index 3f95ef45..b1ed3626 100644
--- a/src/include/PFunction.h
+++ b/src/include/PFunction.h
@@ -123,7 +123,7 @@ class PFunction {
     Int_t fFuncNo; ///< function number, i.e. FUNx with x the function number
 
     virtual void EvalTreeForString(tree_parse_info<> info);
-    virtual void EvalTreeForStringExpression(iter_t const& i);
+    virtual void EvalTreeForStringExpression(iter_t const& i, bool funcFlag=false);
     TString fFuncString; ///< text representation of the function
 
     PMetaData fMetaData; ///< keeps meta data from data files (field, energy, temperature, ...)