diff --git a/aeon/synthesis_grammar/synthesizer.py b/aeon/synthesis_grammar/synthesizer.py
index d86bca47..549ffa2e 100644
--- a/aeon/synthesis_grammar/synthesizer.py
+++ b/aeon/synthesis_grammar/synthesizer.py
@@ -243,7 +243,7 @@ def geneticengine_synthesis(
     """Performs a synthesis procedure with GeneticEngine"""
     # gp_params = gp_params or parse_config("aeon/synthesis_grammar/gpconfig.gengy", "DEFAULT") # TODO
     gp_params = gp_params or gengy_default_config
-
+    gp_params = dict(gp_params)
     representation_name = gp_params.pop("representation")
     config_name = gp_params.pop("config_name")
     seed = gp_params["seed"]
diff --git a/tests/synth_fitness_test.py b/tests/synth_fitness_test.py
index d55938f6..61a6f32e 100644
--- a/tests/synth_fitness_test.py
+++ b/tests/synth_fitness_test.py
@@ -2,18 +2,21 @@
 
 from abc import ABC
 
+from aeon.__main__ import apply_decorators_in_program
 from aeon.core.terms import Term
 from aeon.core.types import top
 from aeon.frontend.anf_converter import ensure_anf
+from aeon.logger.logger import setup_logger
 from aeon.sugar.desugar import desugar
 from aeon.sugar.parser import parse_program
 from aeon.synthesis_grammar.grammar import mk_method_core_literal
 from aeon.synthesis_grammar.synthesizer import synthesize
 from aeon.typechecking.typeinfer import check_type_errors
 
+setup_logger()
 
-def mock_literal_individual(value: int):
 
+def mock_literal_individual(value: int):
     class t_Int(ABC):
         pass
 
@@ -29,10 +32,9 @@ def __init__(self, value: int):
 
 
 def test_fitness():
-    code = """
-        def year : Int = 2023;
-        def synth : Int = (?hole: Int) * 7;
-        def __internal__fitness_function_synth : Int  =  year - synth;
+    code = """def year : Int = 2023;
+        def synth (i: Int): Int { (?hole: Int) * i}
+        def __internal__fitness_function_synth : Int  =  year - synth(7);
     """
     prog = parse_program(code)
     p, ctx, ectx = desugar(prog)
@@ -41,3 +43,18 @@ def __internal__fitness_function_synth : Int  =  year - synth;
     term = synthesize(ctx, ectx, p, [("synth", ["hole"])])
 
     assert isinstance(term, Term)
+
+
+def test_fitness2():
+    code = """def year : Int = 2023;
+            @minimize_int( year - synth(7) )
+            def synth (i:Int) : Int {(?hole: Int) * i}
+        """
+    prog = parse_program(code)
+    prog = apply_decorators_in_program(prog)
+    p, ctx, ectx = desugar(prog)
+    p = ensure_anf(p)
+    check_type_errors(ctx, p, top)
+    term = synthesize(ctx, ectx, p, [("synth", ["hole"])])
+
+    assert isinstance(term, Term)