diff --git a/include/mp/solver-opt.h b/include/mp/solver-opt.h
index f07f7ff46..901e4935b 100644
--- a/include/mp/solver-opt.h
+++ b/include/mp/solver-opt.h
@@ -180,7 +180,7 @@ class SolverOption {
   ValueArrayRef values() const { return values_; }
 
   /// Returns true if this option is a flag, i.e. it doesn't take a value.
-  bool is_flag() const { return is_flag_; }
+  virtual bool is_flag() const { return is_flag_; }
 
   /// Returns the option value.
   virtual void GetValue(fmt::LongLong &) const {
@@ -312,7 +312,7 @@ class TypedSolverOption : public SolverOption {
                     ValueArrayRef values = ValueArrayRef())
     : SolverOption(name, description, values) {}
 
-  void Write(fmt::Writer &w) { w << GetValue<T>(); }
+  void Write(fmt::Writer &w) override { w << GetValue<T>(); }
 
   /// Parses the string for an option value, throws an exception if the value
   /// is invalid.
@@ -322,7 +322,7 @@ class TypedSolverOption : public SolverOption {
   ///                     so it is now in the format of null terminated substrings.
   ///                     If parsed from the environment variable, the string is
   ///                     monolithic, space separated and quotes have to be considered.
-  void Parse(const char *&s, bool splitString=false) {
+  void Parse(const char *&s, bool splitString=false) override {
     const char *start = s;
     T value = internal::OptionHelper<T>::Parse(s, splitString);
     if (*s && !std::isspace(*s)) {
@@ -333,7 +333,7 @@ class TypedSolverOption : public SolverOption {
     SetValue(value);
   }
 
-  virtual Option_Type type() {
+  virtual Option_Type type() override {
     if (std::is_integral<T>::value)
       return Option_Type::INT;
     if (std::is_arithmetic<T>::value)
@@ -489,7 +489,8 @@ class SolverOptionManager {
 
 
 public:
-  /// Stored option: references a variable
+  /// Stored option: references a variable.
+  /// StoredOption<bool> is specialized.
   template <class Value>
   class StoredOption : public mp::TypedSolverOption<Value> {
     Value& value_;
@@ -497,7 +498,8 @@ class SolverOptionManager {
     using value_type = Value;
     StoredOption(const char *name_list, const char *description,
                  Value& v, ValueArrayRef values = ValueArrayRef())
-      : mp::TypedSolverOption<Value>(name_list, description, values), value_(v) {}
+      : mp::TypedSolverOption<Value>(name_list, description, values),
+        value_(v) {}
 
     void GetValue(Value &v) const override { v = value_; }
     void SetValue(typename internal::OptionHelper<Value>::Arg v) override
@@ -795,9 +797,36 @@ class SolverOptionManager {
   set_option_iterator set_option_end() const {
     return set_option_iterator(options_.end());
   }
-  ~SolverOptionManager();
+  virtual ~SolverOptionManager();
 };
 
+
+/// Stored option <bool>.
+/// Can only be set to True.
+template <>
+class SolverOptionManager::StoredOption<bool>
+    : public mp::TypedSolverOption<int> {
+  bool& value_;
+public:
+  using value_type = bool;
+  StoredOption(const char *name_list, const char *description,
+               bool& v, ValueArrayRef values = ValueArrayRef())
+    : mp::TypedSolverOption<int>(name_list, description, values),
+      value_(v) {}
+
+  /// We are a flag
+  bool is_flag() const override { return true; }
+
+  /// Parse: only set to True
+  void Parse(const char *&, bool =false) override
+  { value_ = true; }
+
+  /// Dummy
+  void GetValue(int &v) const override { v = value_; }
+  void SetValue(int v) override { value_ = v; }
+};
+
+
 }  // namespace mp
 
 #endif // SOLVEROPT_H
diff --git a/solvers/visitor/visitorbackend.cc b/solvers/visitor/visitorbackend.cc
index 66496ab2a..984465f6f 100644
--- a/solvers/visitor/visitorbackend.cc
+++ b/solvers/visitor/visitorbackend.cc
@@ -337,16 +337,22 @@ void VisitorBackend::InitCustomOptions() {
       "\n"
       "  ampl: option visitor_options 'mipgap=1e-6';\n");
 
+  // Use AddSolverOption() for proper solver parameters.
+  // Below are examples of options stored in variables for own use.
+
   AddStoredOption("tech:option_example opt_example example_opt",
       "Example option. "
       "Default = \"\" (don't work too hard).",
       storedOptions_.option_example_);
 
+  AddStoredOption("tech:flag1 flag1",
+      "Flag option. Use without value. Can only be set to True.",
+      storedOptions_.flag_option_);
+
   AddListOption("tech:list_option opt_list multi_valued_option",
       "Multi-valued option when repeated.",
       storedOptions_.list_option_);
 
-  // Use AddSolverOption() for solver parameters
 }
 
 
diff --git a/solvers/visitor/visitorbackend.h b/solvers/visitor/visitorbackend.h
index d93616945..2e962debf 100644
--- a/solvers/visitor/visitorbackend.h
+++ b/solvers/visitor/visitorbackend.h
@@ -179,6 +179,7 @@ class VisitorBackend :
   /// These options are stored in the class
   struct Options {
     std::string option_example_;
+    bool flag_option_ = false;
     std::vector<double> list_option_;
   };
   Options storedOptions_;
diff --git a/solvers/xpress/xpressbackend.cc b/solvers/xpress/xpressbackend.cc
index 70da55589..4ac37dc94 100644
--- a/solvers/xpress/xpressbackend.cc
+++ b/solvers/xpress/xpressbackend.cc
@@ -219,7 +219,7 @@ std::string XpressmpBackend::XPRESSSolveFlags() {
   if (bool(storedOptions_.fBarrier_)
       + bool(storedOptions_.fPrimal_)
       + bool(storedOptions_.fDual_)
-      + bool(storedOptions_.fNetwork_)) {
+      + bool(storedOptions_.fNetwork_) >= 2) {
     AddWarning("Ambiguous LP method",
                "Only one of barrier/primal/dual/network should be specified.");
   }
diff --git a/solvers/xpress/xpressbackend.h b/solvers/xpress/xpressbackend.h
index 77f83d447..6e725a8ff 100644
--- a/solvers/xpress/xpressbackend.h
+++ b/solvers/xpress/xpressbackend.h
@@ -211,10 +211,10 @@ class XpressmpBackend :
     int pooldupcol_;
     int poollimit_ = 10;
     int nPoolMode_ = 0;
-    int fBarrier_ = 0;
-    int fPrimal_ = 0;
-    int fDual_ = 0;
-    int fNetwork_ = 0;
+    bool fBarrier_ = 0;
+    bool fPrimal_ = 0;
+    bool fDual_ = 0;
+    bool fNetwork_ = 0;
     std::string tunebase_;
     std::string tunename_;
     std::string logFile_;
diff --git a/test/end2end/cases/categorized/fast/tech/modellist.json b/test/end2end/cases/categorized/fast/tech/modellist.json
index 476284505..9698b5bab 100644
--- a/test/end2end/cases/categorized/fast/tech/modellist.json
+++ b/test/end2end/cases/categorized/fast/tech/modellist.json
@@ -18,5 +18,12 @@
       "solve_result_num": 500,
       "solve_exitcode":   0
     }
+  },
+  {
+    "name" : "Check_Barrier_Flag",
+    "tags" : ["option_flag_barrier"],
+    "files" : ["diet.mod", "diet.dat"],
+    "options": { "ANYSOLVER_options": "outlev 1 barrier outlev 0" },
+    "objective": 88.2
   }
 ]
diff --git a/test/end2end/scripts/python/Model.py b/test/end2end/scripts/python/Model.py
index d6f69f0ef..f28b84292 100644
--- a/test/end2end/scripts/python/Model.py
+++ b/test/end2end/scripts/python/Model.py
@@ -75,6 +75,9 @@ class ModelTags(enum.Enum):
     check_sos2_from_pl = 51000           # Solvers accepting SOS2 constraints but wishing
                                          # to test SOS2 conversion, by acc:sos2=1
 
+    ## Specific options (e.g., XPRESS)
+    option_flag_barrier = 61000
+
     ## Solver-specific
     gurobi_cloud = 100000
     gurobi_server=100001
diff --git a/test/end2end/scripts/python/Solver.py b/test/end2end/scripts/python/Solver.py
index 5cef18b33..6fe424520 100644
--- a/test/end2end/scripts/python/Solver.py
+++ b/test/end2end/scripts/python/Solver.py
@@ -721,6 +721,8 @@ def __init__(self, exeName, timeout=None, nthreads=None,
                  
                  ModelTags.writelp, ModelTags.writesol,
 
+                 ModelTags.option_flag_barrier,
+
                  }
         super().__init__(exeName, timeout, nthreads, otherOptions, stags)