diff --git a/src/embed_tests/Codecs.cs b/src/embed_tests/Codecs.cs
index be416bc15..9b764d43f 100644
--- a/src/embed_tests/Codecs.cs
+++ b/src/embed_tests/Codecs.cs
@@ -355,6 +355,19 @@ from datetime import datetime
             scope.Exec("Codecs.AcceptsDateTime(datetime(2021, 1, 22))");
         }
 
+        [Test]
+        public void FloatDerivedDecoded()
+        {
+            using var scope = Py.CreateScope();
+            scope.Exec(@"class FloatDerived(float): pass");
+            using var floatDerived = scope.Eval("FloatDerived");
+            var decoder = new DecoderReturningPredefinedValue<object>(floatDerived, 42);
+            PyObjectConversions.RegisterDecoder(decoder);
+            using var result = scope.Eval("FloatDerived()");
+            object decoded = result.As<object>();
+            Assert.AreEqual(42, decoded);
+        }
+
         [Test]
         public void ExceptionDecodedNoInstance()
         {
diff --git a/src/runtime/Converter.cs b/src/runtime/Converter.cs
index 3c46e9034..73bbd4a3a 100644
--- a/src/runtime/Converter.cs
+++ b/src/runtime/Converter.cs
@@ -361,28 +361,44 @@ internal static bool ToManagedValue(BorrowedReference value, Type obType,
             // conversions (Python string -> managed string).
             if (obType == objectType)
             {
-                if (Runtime.PyString_Check(value))
+                if (Runtime.PyString_CheckExact(value))
                 {
                     return ToPrimitive(value, stringType, out result, setError);
                 }
 
-                if (Runtime.PyBool_Check(value))
+                if (Runtime.PyBool_CheckExact(value))
                 {
                     return ToPrimitive(value, boolType, out result, setError);
                 }
 
-                if (Runtime.PyFloat_Check(value))
+                if (Runtime.PyFloat_CheckExact(value))
                 {
                     return ToPrimitive(value, doubleType, out result, setError);
                 }
 
-                // give custom codecs a chance to take over conversion of ints and sequences
+                // give custom codecs a chance to take over conversion
+                // of ints, sequences, and types derived from primitives
                 BorrowedReference pyType = Runtime.PyObject_TYPE(value);
                 if (PyObjectConversions.TryDecode(value, pyType, obType, out result))
                 {
                     return true;
                 }
 
+                if (Runtime.PyString_Check(value))
+                {
+                    return ToPrimitive(value, stringType, out result, setError);
+                }
+
+                if (Runtime.PyBool_Check(value))
+                {
+                    return ToPrimitive(value, boolType, out result, setError);
+                }
+
+                if (Runtime.PyFloat_Check(value))
+                {
+                    return ToPrimitive(value, doubleType, out result, setError);
+                }
+
                 if (Runtime.PyInt_Check(value))
                 {
                     result = new PyInt(value);
diff --git a/src/runtime/Runtime.cs b/src/runtime/Runtime.cs
index 6238119ff..7110f3cb0 100644
--- a/src/runtime/Runtime.cs
+++ b/src/runtime/Runtime.cs
@@ -1094,8 +1094,13 @@ internal static nint PyBuffer_SizeFromFormat(string format)
         internal static bool PyInt_Check(BorrowedReference ob)
             => PyObject_TypeCheck(ob, PyLongType);
 
+        internal static bool PyInt_CheckExact(BorrowedReference ob)
+            => PyObject_TypeCheckExact(ob, PyLongType);
+
         internal static bool PyBool_Check(BorrowedReference ob)
             => PyObject_TypeCheck(ob, PyBoolType);
+        internal static bool PyBool_CheckExact(BorrowedReference ob)
+            => PyObject_TypeCheckExact(ob, PyBoolType);
 
         internal static NewReference PyInt_FromInt32(int value) => PyLong_FromLongLong(value);
 
@@ -1141,6 +1146,8 @@ internal static NewReference PyLong_FromString(string value, int radix)
 
         internal static bool PyFloat_Check(BorrowedReference ob)
             => PyObject_TypeCheck(ob, PyFloatType);
+        internal static bool PyFloat_CheckExact(BorrowedReference ob)
+            => PyObject_TypeCheckExact(ob, PyFloatType);
 
         /// <summary>
         /// Return value: New reference.
@@ -1282,9 +1289,9 @@ internal static bool PyFloat_Check(BorrowedReference ob)
         // Python string API
         //====================================================================
         internal static bool PyString_Check(BorrowedReference ob)
-        {
-            return PyObject_TYPE(ob) == PyStringType;
-        }
+            => PyObject_TypeCheck(ob, PyStringType);
+        internal static bool PyString_CheckExact(BorrowedReference ob)
+            => PyObject_TypeCheckExact(ob, PyStringType);
 
         internal static NewReference PyString_FromString(string value)
         {
@@ -1643,6 +1650,8 @@ internal static bool PyType_IsSubtype(BorrowedReference t1, BorrowedReference t2
             return Delegates.PyType_IsSubtype(t1, t2);
         }
 
+        internal static bool PyObject_TypeCheckExact(BorrowedReference ob, BorrowedReference tp)
+            => PyObject_TYPE(ob) == tp;
         internal static bool PyObject_TypeCheck(BorrowedReference ob, BorrowedReference tp)
         {
             BorrowedReference t = PyObject_TYPE(ob);