diff --git a/kernel_tuner/strategies/wrapper.py b/kernel_tuner/strategies/wrapper.py
index d6d91f2d..df45d867 100644
--- a/kernel_tuner/strategies/wrapper.py
+++ b/kernel_tuner/strategies/wrapper.py
@@ -34,6 +34,13 @@ def __init__(self, optimizer: OptAlg):
         self.optimizer: OptAlg = optimizer
 
     def tune(self, searchspace: Searchspace, runner, tuning_options):
+        if not hasattr(self.optimizer, 'costfunc_kwargs'):
+            # Set costfunc kwarts to no scaling and no snapping (assume a mixed-int optimizer).
+            self.optimizer.costfunc_kwargs = {
+                "scaling": False,
+                "snap": False,
+            }
+            self.optimizer.constraint_aware = False
         cost_func = CostFunc(searchspace, tuning_options, runner, **self.optimizer.costfunc_kwargs)
 
         if self.optimizer.costfunc_kwargs.get('scaling', False):
diff --git a/pyproject.toml b/pyproject.toml
index 0565f571..b9ba6b89 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,11 +50,11 @@ classifiers = [
 # ATTENTION: if anything is changed here, run `poetry update`
 requires-python = ">=3.10,<4" # <4 is because of hip-python  # NOTE when changing the Python versions, also change the test versions in the Noxfile and GitHub Actions
 dependencies = [
-    "numpy>=2.0.0",
+    "numpy (>=1.26.0,<2.0.0)",
     "scipy>=1.14.1",    # Python >=3.13 needs scipy >=1.14
     "packaging",        # required by file_utils
     "jsonschema",
-    "python-constraint2>=2.3.1",
+    "python-constraint2>=2.2.2",
     "xmltodict",
     "pandas>=2.0.0",
     "scikit-learn>=1.0.2",