diff --git a/ComputingTasks.cc b/ComputingTasks.cc
index f08af505..3b60d79e 100644
--- a/ComputingTasks.cc
+++ b/ComputingTasks.cc
@@ -1047,5 +1047,8 @@ void
 PlotConditionalForecastStatement::writeOutput(ostream &output, const string &basename) const
 {
   symbol_list.writeOutput("var_list_", output);
-  output << "plot_icforecast(var_list_);" << endl;
+  if (periods == -1)
+    output << "plot_icforecast(var_list_);" << endl;
+  else
+    output << "plot_icforecast(var_list_, " << periods << ");" << endl;
 }
diff --git a/ComputingTasks.hh b/ComputingTasks.hh
index 1ba0f707..8529acd2 100644
--- a/ComputingTasks.hh
+++ b/ComputingTasks.hh
@@ -481,7 +481,7 @@ public:
 class PlotConditionalForecastStatement : public Statement
 {
 private:
-  //! A value of -1 indicates that the length of the constrained path should be used
+  //! A value of -1 indicates that the user didn't specify a value
   const int periods;
   const SymbolList symbol_list;
 public: