diff --git a/gillespy2/core/model.py b/gillespy2/core/model.py
index 1ff76dfb..b29437fa 100644
--- a/gillespy2/core/model.py
+++ b/gillespy2/core/model.py
@@ -1295,6 +1295,8 @@ def run(self, solver=None, timeout=0, t=None, increment=None, algorithm=None, **
                 if "CSolver" in solver.name and \
                     ("resume" in solver_args or "variables" in solver_args or "live_output" in solver_args):
                     sol_kwargs['variable'] = True
+                if "build_definitions" in solver_args:
+                    sol_kwargs['build_definitions'] = solver_args['build_definitions']
                 solver = solver(**sol_kwargs)
             except Exception as err:
                 raise SimulationError(f"{solver} is not a valid solver.  Reason Given: {err}.") from err
diff --git a/gillespy2/solvers/cpp/build/SConstruct b/gillespy2/solvers/cpp/build/SConstruct
index f5b4eb65..18712e9d 100644
--- a/gillespy2/solvers/cpp/build/SConstruct
+++ b/gillespy2/solvers/cpp/build/SConstruct
@@ -51,6 +51,9 @@ env = Environment(
     # When MSVC (or any other compilers) are supported, update this to be a compiler-specific flag
     CXXFLAGS=['-std=c++14'],
 )
+extra_cxxflags = ARGUMENTS.get('EXTRA_CXXFLAGS', '')
+if extra_cxxflags:
+    env.Append(CXXFLAGS=extra_cxxflags.split())
 libdepends = [
     f'gpy{solver}',
     'gpystd'
diff --git a/gillespy2/solvers/cpp/c_solver.py b/gillespy2/solvers/cpp/c_solver.py
index 30d1b612..79578d07 100644
--- a/gillespy2/solvers/cpp/c_solver.py
+++ b/gillespy2/solvers/cpp/c_solver.py
@@ -59,10 +59,13 @@ class CSolver:
 
     :param variable: Indicates whether the simulation should be variable.
     :type variable: bool
+
+    :param build_definitions: Dictionary of definitions to be passed to the build engine (e.g. {'cxxflags':'-O3'})
+    :type build_definitions: "dict[str, str]"
     """
     rc = 0
 
-    def __init__(self, model: Model = None, output_directory: str = None, delete_directory: bool = True, resume=None, variable: bool = False):
+    def __init__(self, model: Model = None, output_directory: str = None, delete_directory: bool = True, resume=None, variable: bool = False, build_definitions: "dict[str, str]" = None):
         if model is None:
             raise gillespyError.SimulationError("A model is required to run the simulation.")
 
@@ -79,6 +82,7 @@ def __init__(self, model: Model = None, output_directory: str = None, delete_dir
         self.resume = resume
         self.variable = variable
         self.build_engine: BuildEngine = None
+        self.build_definitions: "dict[str, str]" = build_definitions
 
         # Validate output_directory, ensure that it doesn't already exist
         if isinstance(output_directory, str):
@@ -106,7 +110,7 @@ def __del__(self):
 
         self.build_engine.clean()
 
-    def _build(self, model: "Union[Model, SanitizedModel]", simulation_name: str, variable: bool, debug: bool = False) -> str:
+    def _build(self, model: "Union[Model, SanitizedModel]", simulation_name: str, variable: bool, debug: bool = False, build_definitions: "dict[str, str]" = None) -> str:
         """
         Generate and build the simulation from the specified Model and solver_name into the output_dir.
 
@@ -128,7 +132,7 @@ def _build(self, model: "Union[Model, SanitizedModel]", simulation_name: str, va
             self.build_engine = BuildEngine(debug=debug, output_dir=self.output_directory)
             self.build_engine.prepare(model, variable)
             # Compile the simulation, returning the path of the executable.
-            return self.build_engine.build_simulation(simulation_name)
+            return self.build_engine.build_simulation(simulation_name, build_definitions)
 
         # Assume that the simulation has already been built.
         return self.build_engine.get_executable_path()
@@ -336,7 +340,7 @@ def _set_model(self, model=None):
         if model is not None:
             self.model = copy.deepcopy(model)
 
-        self._build(self.model, self.target, self.variable, False)
+        self._build(self.model, self.target, self.variable, False, self.build_definitions)
         self.species_mappings = self.model.sanitized_species_names()
         self.species = list(self.species_mappings.keys())
         self.parameter_mappings = self.model.sanitized_parameter_names()
diff --git a/gillespy2/solvers/cpp/ssa_c_solver.py b/gillespy2/solvers/cpp/ssa_c_solver.py
index 098d2d38..f0f6befd 100644
--- a/gillespy2/solvers/cpp/ssa_c_solver.py
+++ b/gillespy2/solvers/cpp/ssa_c_solver.py
@@ -43,7 +43,8 @@ def get_solver_settings(cls):
 
     def run(self=None, model: Model = None, t: int = None, number_of_trajectories: int = 1, timeout: int = 0,
             increment: int = None, seed: int = None, debug: bool = False, profile: bool = False, variables={},
-            resume=None, live_output: str = None, live_output_options: dict = {}, **kwargs):
+            resume=None, live_output: str = None, live_output_options: dict = {},
+            build_definitions: "dict[str, str]" = None, **kwargs):
 
         from gillespy2 import log
 
@@ -182,4 +183,4 @@ def run(self=None, model: Model = None, t: int = None, number_of_trajectories: i
         self.result = simulation_data
         self.rc = int(sim_status)
 
-        return Results.build_from_solver_results(self, live_output_options)
\ No newline at end of file
+        return Results.build_from_solver_results(self, live_output_options)