diff --git a/src/runtime/Converter.cs b/src/runtime/Converter.cs
@@ -710,7 +710,7 @@ internal static bool ToPrimitive(BorrowedReference value, Type obType, out objec
                     {
                         if (Runtime.Is32Bit)
                         {
-                            if (!Runtime.PyLong_Check(value))
+                            if (!Runtime.PyInt_Check(value))
                             {
                                 goto type_error;
                             }

diff --git a/src/runtime/Runtime.cs b/src/runtime/Runtime.cs
@@ -1101,11 +1101,6 @@ internal static bool PyBool_Check(BorrowedReference ob)
 
         internal static NewReference PyInt_FromInt64(long value) => PyLong_FromLongLong(value);
 
-        internal static bool PyLong_Check(BorrowedReference ob)
-        {
-            return PyObject_TYPE(ob) == PyLongType;
-        }
-
         internal static NewReference PyLong_FromLongLong(long value) => Delegates.PyLong_FromLongLong(value);
 
 
@@ -1145,9 +1140,7 @@ internal static NewReference PyLong_FromString(string value, int radix)
         }
 
         internal static bool PyFloat_Check(BorrowedReference ob)
-        {
-            return PyObject_TYPE(ob) == PyFloatType;
-        }
+            => PyObject_TypeCheck(ob, PyFloatType);
 
         /// <summary>
         /// Return value: New reference.

diff --git a/tests/test_method.py b/tests/test_method.py
@@ -1256,3 +1256,41 @@ def test_method_encoding():
 def test_method_with_pointer_array_argument():
     with pytest.raises(TypeError):
         MethodTest.PointerArray([0])
+
+def test_method_call_implicit_conversion():
+
+    class IntAnswerMixin:
+        # For Python >= 3.8
+        def __index__(self):
+            return 42
+
+        # For Python < 3.10
+        def __int__(self):
+            return 42
+
+    class Answer(int, IntAnswerMixin):
+        pass
+
+    class FloatAnswer(float, IntAnswerMixin):
+        def __float__(self):
+            return 42.0
+
+    # TODO: This should also work for integer types but due to some complexities
+    # in the C-API functions (some call __int__/__index__, some don't), it's not
+    # supported, yet.
+    for v in [Answer(), FloatAnswer()]:
+        for t in [System.Double, System.Single]:
+            min_value = t(t.MinValue)
+            compare_to = min_value.CompareTo.__overloads__[t]
+
+            assert compare_to(v) == -1
+
+    class SomeNonFloat:
+        def __float__(self):
+            return 42.0
+
+    for t in [System.Double, System.Single]:
+        with pytest.raises(TypeError):
+            min_value = t(t.MinValue)
+            compare_to = min_value.CompareTo.__overloads__[t]
+            assert compare_to(SomeNonFloat()) == -1