diff --git a/src/optimagic/optimization/algorithm.py b/src/optimagic/optimization/algorithm.py
index 334c40daf..f3188533a 100644
--- a/src/optimagic/optimization/algorithm.py
+++ b/src/optimagic/optimization/algorithm.py
@@ -14,7 +14,7 @@
 from optimagic.optimization.internal_optimization_problem import (
     InternalOptimizationProblem,
 )
-from optimagic.type_conversion import TYPE_CONVERTERS
+from optimagic.type_conversion import TYPE_CONVERTERS, TYPE_CONVERTERS_BY_NAME
 from optimagic.typing import AggregationLevel
 
 
@@ -219,10 +219,16 @@ def _solve_internal_problem(
     def __post_init__(self) -> None:
         for field in self.__dataclass_fields__:
             raw_value = getattr(self, field)
-            target_type = typing.cast(type, self.__dataclass_fields__[field].type)
-            if target_type in TYPE_CONVERTERS:
+            target_type = self.__dataclass_fields__[field].type
+            # In modules with `from __future__ import annotations`, field types
+            # are annotation strings rather than type objects.
+            if isinstance(target_type, str):
+                converter = TYPE_CONVERTERS_BY_NAME.get(target_type)
+            else:
+                converter = TYPE_CONVERTERS.get(typing.cast(type, target_type))
+            if converter is not None:
                 try:
-                    value = TYPE_CONVERTERS[target_type](raw_value)
+                    value = converter(raw_value)
                 except (KeyboardInterrupt, SystemExit):
                     raise
                 except Exception as e:
diff --git a/src/optimagic/type_conversion.py b/src/optimagic/type_conversion.py
index d9d5506ac..9cbb0753d 100644
--- a/src/optimagic/type_conversion.py
+++ b/src/optimagic/type_conversion.py
@@ -87,3 +87,17 @@ def _process_bool_like(value: Any) -> bool:
     NonNegativeFloat: _process_non_negative_float_like,
     GtOneFloat: _process_gt_one_float_like,
 }
+
+# In modules with `from __future__ import annotations`, dataclass field types are
+# annotation strings rather than type objects, so converter lookups need a
+# name-based mapping.
+TYPE_CONVERTERS_BY_NAME = {
+    "float": _process_float_like,
+    "int": _process_int_like,
+    "bool": _process_bool_like,
+    "PositiveInt": _process_positive_int_like,
+    "NonNegativeInt": _process_non_negative_int_like,
+    "PositiveFloat": _process_positive_float_like,
+    "NonNegativeFloat": _process_non_negative_float_like,
+    "GtOneFloat": _process_gt_one_float_like,
+}
diff --git a/tests/optimagic/optimization/test_algorithm.py b/tests/optimagic/optimization/test_algorithm.py
index 71bae8a79..251078947 100644
--- a/tests/optimagic/optimization/test_algorithm.py
+++ b/tests/optimagic/optimization/test_algorithm.py
@@ -1,8 +1,9 @@
-from dataclasses import dataclass
+from dataclasses import dataclass, fields
 
 import numpy as np
 import pytest
 
+from optimagic.algorithms import ALL_ALGORITHMS
 from optimagic.exceptions import InvalidAlgoInfoError, InvalidAlgoOptionError
 from optimagic.optimization.algorithm import AlgoInfo, Algorithm, InternalOptimizeResult
 from optimagic.optimization.history import HistoryEntry
@@ -10,6 +11,7 @@
     AggregationLevel,
     EvalTask,
     NonNegativeFloat,
+    NonNegativeInt,
     PositiveFloat,
     PositiveInt,
 )
@@ -198,6 +200,16 @@ def test_with_option_if_applicable():
 # ======================================================================================
 
 
+def test_field_types_are_type_objects():
+    # Guard: this module must NOT use `from __future__ import annotations`,
+    # otherwise the tests below no longer cover the type-object code path of the
+    # option conversion. The stringified-annotations path is covered in
+    # test_algorithm_future_annotations.py.
+    field_types = {f.name: f.type for f in fields(DummyAlgorithm)}
+    assert field_types["stopping_maxiter"] == PositiveInt
+    assert field_types["initial_radius"] == PositiveFloat
+
+
 def test_algorithm_does_type_conversion():
     algo = DummyAlgorithm(
         initial_radius="1.0",
@@ -229,6 +241,61 @@ def test_algorithm_does_type_conversion_in_with_option():
     assert new_algo.max_radius == 20.0
 
 
+def test_algorithm_converts_float_to_int():
+    algo = DummyAlgorithm(stopping_maxiter=1000.0)
+    assert isinstance(algo.stopping_maxiter, int)
+    assert algo.stopping_maxiter == 1000
+
+
 def test_error_with_negative_radius():
     with pytest.raises(Exception):  # noqa: B017
         DummyAlgorithm(initial_radius=-1.0)
+
+
+# ======================================================================================
+# Test type conversion works for all registered algorithms
+# ======================================================================================
+
+# Field types are type objects in modules without `from __future__ import
+# annotations` and annotation strings in modules with it. Both must be coerced.
+INT_ANNOTATIONS = (
+    int,
+    PositiveInt,
+    NonNegativeInt,
+    "int",
+    "PositiveInt",
+    "NonNegativeInt",
+)
+
+
+def _int_options_with_int_defaults(cls):
+    out = {}
+    for field in fields(cls):
+        has_int_annotation = any(field.type == t for t in INT_ANNOTATIONS)
+        has_int_default = isinstance(field.default, int) and not isinstance(
+            field.default, bool
+        )
+        if has_int_annotation and has_int_default:
+            out[field.name] = field.default
+    return out
+
+
+@pytest.mark.parametrize("cls", ALL_ALGORITHMS.values(), ids=ALL_ALGORITHMS.keys())
+def test_int_options_are_coerced_for_all_algorithms(cls):
+    """Passing floats for int-typed options must result in int attributes.
+
+    This guards against the option conversion in Algorithm.__post_init__ being
+    silently skipped, as happened for optimizer modules with postponed annotations
+    where the field type is a string rather than a type object.
+
+    """
+    int_options = _int_options_with_int_defaults(cls)
+    if not int_options:
+        pytest.skip("Algorithm has no int-typed options with int defaults.")
+
+    algo = cls(**{name: float(default) for name, default in int_options.items()})
+
+    for name, default in int_options.items():
+        value = getattr(algo, name)
+        assert isinstance(value, int), f"Option {name} was not coerced to int."
+        assert value == default
diff --git a/tests/optimagic/optimization/test_algorithm_future_annotations.py b/tests/optimagic/optimization/test_algorithm_future_annotations.py
new file mode 100644
index 000000000..1f1beb144
--- /dev/null
+++ b/tests/optimagic/optimization/test_algorithm_future_annotations.py
@@ -0,0 +1,99 @@
+"""Test algo option type conversion in modules with postponed annotations.
+
+With `from __future__ import annotations`, dataclass field types are annotation
+strings rather than type objects. This silently disabled the type conversion in
+`Algorithm.__post_init__` for all optimizer modules using the import. The tests in
+this module mirror the type conversion tests in test_algorithm.py for a dummy
+algorithm defined under postponed annotations; test_algorithm.py covers the case
+without the import.
+
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, fields
+
+import pytest
+
+from optimagic.exceptions import InvalidAlgoOptionError
+from optimagic.optimization.algorithm import Algorithm, InternalOptimizeResult
+from optimagic.optimization.history import HistoryEntry
+from optimagic.typing import (
+    EvalTask,
+    NonNegativeFloat,
+    PositiveFloat,
+    PositiveInt,
+)
+
+
+@dataclass(frozen=True)
+class DummyAlgorithm(Algorithm):
+    initial_radius: PositiveFloat = 1.0
+    max_radius: PositiveFloat = 10.0
+    convergence_ftol_rel: NonNegativeFloat = 1e-6
+    stopping_maxiter: PositiveInt = 1000
+
+    def _solve_internal_problem(self, problem, x0):
+        hist_entry = HistoryEntry(
+            params=x0,
+            fun=0.0,
+            start_time=0.0,
+            task=EvalTask.FUN,
+        )
+        problem.history.add_entry(hist_entry)
+        return InternalOptimizeResult(x=x0, fun=0.0, success=True)
+
+
+def test_field_types_are_annotation_strings():
+    # Guard: this module must keep `from __future__ import annotations`, otherwise
+    # the tests below no longer cover the stringified-annotations code path.
+    field_types = {f.name: f.type for f in fields(DummyAlgorithm)}
+    assert field_types["stopping_maxiter"] == "PositiveInt"
+    assert field_types["initial_radius"] == "PositiveFloat"
+
+
+def test_algorithm_does_type_conversion():
+    algo = DummyAlgorithm(
+        initial_radius="1.0",
+        max_radius="10.0",
+        convergence_ftol_rel="1e-6",
+        stopping_maxiter="1000",
+    )
+
+    assert isinstance(algo.initial_radius, float)
+    assert algo.initial_radius == 1.0
+    assert isinstance(algo.max_radius, float)
+    assert algo.max_radius == 10.0
+    assert isinstance(algo.convergence_ftol_rel, float)
+    assert algo.convergence_ftol_rel == 1e-6
+    assert isinstance(algo.stopping_maxiter, int)
+    assert algo.stopping_maxiter == 1000
+
+
+def test_algorithm_converts_float_to_int():
+    algo = DummyAlgorithm(stopping_maxiter=1000.0)
+    assert isinstance(algo.stopping_maxiter, int)
+    assert algo.stopping_maxiter == 1000
+
+
+def test_algorithm_does_type_conversion_in_with_option():
+    algo = DummyAlgorithm()
+    new_algo = algo.with_option(
+        initial_radius="2.0",
+        max_radius="20.0",
+    )
+
+    assert isinstance(new_algo.initial_radius, float)
+    assert new_algo.initial_radius == 2.0
+    assert isinstance(new_algo.max_radius, float)
+    assert new_algo.max_radius == 20.0
+
+
+def test_error_with_negative_radius():
+    with pytest.raises(InvalidAlgoOptionError):
+        DummyAlgorithm(initial_radius=-1.0)
+
+
+def test_error_with_negative_maxiter():
+    with pytest.raises(InvalidAlgoOptionError):
+        DummyAlgorithm(stopping_maxiter=-1)