diff --git a/gigaevo/programs/stages/optimization/optuna/desubstitution.py b/gigaevo/programs/stages/optimization/optuna/desubstitution.py
index ae42457f..36dbff18 100644
--- a/gigaevo/programs/stages/optimization/optuna/desubstitution.py
+++ b/gigaevo/programs/stages/optimization/optuna/desubstitution.py
@@ -41,7 +41,7 @@ def _coerce_param_value(value: Any) -> Any:
     if isinstance(value, str):
         try:
             parsed = ast.literal_eval(value)
-        except (ValueError, SyntaxError):
+        except (ValueError, SyntaxError, MemoryError, RecursionError, TypeError):
             return value
         # Coerce whole-number floats to int so range()/indexing works
         if isinstance(parsed, float) and parsed == int(parsed):
@@ -229,16 +229,16 @@ def _clean_eval_in_source(code: str) -> str:
             # Quoted string: eval('math.sqrt') — only strip if dotted name
             try:
                 string_val = ast.literal_eval(inner)
-            except (ValueError, SyntaxError):
+            except (ValueError, SyntaxError, MemoryError, RecursionError, TypeError):
                 continue
             if isinstance(string_val, str) and _DOTTED_NAME_RE.match(string_val):
                 replacement = string_val
         else:
-            # Unquoted: eval([2, 3]), eval((1, 2)), eval(42), etc.
+            # Unquoted: eval([2, 3]), eval((1, 2)), eval(42), eval(-5), etc.
             try:
                 ast.literal_eval(inner)
                 replacement = inner
-            except (ValueError, SyntaxError):
+            except (ValueError, SyntaxError, MemoryError, RecursionError, TypeError):
                 pass
 
         if replacement is not None:
@@ -284,10 +284,15 @@ def visit_Call(self, node: ast.Call) -> ast.AST:
                 return ast.copy_location(result, node)
             return node
 
-        # eval(<literal>) — already a valid AST node, just strip eval()
-        if isinstance(arg, (ast.Constant, ast.List, ast.Tuple, ast.Set, ast.Dict)):
-            return ast.copy_location(arg, node)
-        return node
+        # eval(<literal>) — use ast.literal_eval as the predicate so this
+        # path matches `_clean_eval_in_source` exactly (it also handles
+        # ``UnaryOp(USub|UAdd, Constant)`` like ``eval(-5)``, which the
+        # previous isinstance(...) check silently missed).
+        try:
+            ast.literal_eval(arg)
+        except (ValueError, SyntaxError, MemoryError, RecursionError, TypeError):
+            return node
+        return ast.copy_location(arg, node)
 
 
 # ---------------------------------------------------------------------------
diff --git a/tests/stages/test_desubstitution_edge_cases.py b/tests/stages/test_desubstitution_edge_cases.py
index b5aa8cc0..5555aa24 100644
--- a/tests/stages/test_desubstitution_edge_cases.py
+++ b/tests/stages/test_desubstitution_edge_cases.py
@@ -8,12 +8,15 @@
 
 from __future__ import annotations
 
+import ast
 import textwrap
+from unittest.mock import patch
 
 from gigaevo.programs.stages.optimization.optuna.desubstitution import (
     _build_line_offsets,
     _clean_eval_in_source,
     _coerce_param_value,
+    _EvalCleaner,
     _find_matching_close_paren,
     coerce_params,
     desubstitute_params,
@@ -87,6 +90,55 @@ def test_invalid_string_stays(self) -> None:
         """Strings that cause SyntaxError in literal_eval stay as-is."""
         assert _coerce_param_value("[invalid") == "[invalid"
 
+    def test_literal_eval_memory_error_falls_back(self) -> None:
+        """ast.literal_eval can raise MemoryError on huge literals; the
+        broader except must catch it and return the original string."""
+        target = "gigaevo.programs.stages.optimization.optuna.desubstitution.ast.literal_eval"
+        with patch(target, side_effect=MemoryError):
+            assert _coerce_param_value("[1, 2, 3]") == "[1, 2, 3]"
+
+    def test_literal_eval_recursion_error_falls_back(self) -> None:
+        """Deeply-nested literals can hit RecursionError; same fallback."""
+        target = "gigaevo.programs.stages.optimization.optuna.desubstitution.ast.literal_eval"
+        with patch(target, side_effect=RecursionError):
+            assert _coerce_param_value("[1, 2, 3]") == "[1, 2, 3]"
+
+
+class TestEvalCleanerASTPath:
+    """Direct tests for _EvalCleaner; AST-level eval() stripping."""
+
+    @staticmethod
+    def _strip(code: str) -> str:
+        tree = ast.parse(code)
+        new = _EvalCleaner().visit(tree)
+        ast.fix_missing_locations(new)
+        return ast.unparse(new)
+
+    def test_negative_numeric_literal_is_stripped(self) -> None:
+        """eval(-5) — UnaryOp(USub, Constant) — used to survive because the
+        isinstance check only handled bare Constant/List/Tuple/Set/Dict.
+        Now matches the source-level path."""
+        assert self._strip("x = eval(-5)") == "x = -5"
+        assert self._strip("x = eval(-3.14)") == "x = -3.14"
+
+    def test_non_literal_unaryop_stays(self) -> None:
+        """eval(-some_var) is NOT a literal (operand is Name, not Constant)
+        and must stay wrapped."""
+        assert self._strip("x = eval(-some_var)") == "x = eval(-some_var)"
+
+    def test_eval_of_call_stays(self) -> None:
+        """eval(foo()) is not a literal; must stay wrapped."""
+        assert self._strip("x = eval(foo())") == "x = eval(foo())"
+
+    def test_ast_path_matches_source_path_on_negative_literal(self) -> None:
+        """Parity: AST-path and source-path now produce equivalent output
+        for the previously-divergent eval(-N) case."""
+        code = "x = eval(-5)"
+        ast_out = self._strip(code)
+        src_out = _clean_eval_in_source(code)
+        # Normalize both via ast round-trip for fair textual comparison.
+        assert ast.unparse(ast.parse(ast_out)) == ast.unparse(ast.parse(src_out))
+
 
 class TestCoerceParams:
     def test_dict_coercion(self) -> None: