diff -r 7323bced3d48 Lib/ctypes/test/test_numbers.py
--- a/Lib/ctypes/test/test_numbers.py	Sat Apr 16 18:55:16 2011 +0200
+++ b/Lib/ctypes/test/test_numbers.py	Sat Apr 16 18:50:22 2011 -0500
@@ -82,6 +82,16 @@
             self.assertRaises(TypeError, t, "")
             self.assertRaises(TypeError, t, None)
 
+    def test_float_overflow(self):
+        import sys
+        big_int = int(sys.float_info.max) * 2
+        for t in float_types + [c_longdouble]:
+            self.assertRaises(OverflowError, t, big_int)
+            if (hasattr(t, "__ctype_be__")):
+                self.assertRaises(OverflowError, t.__ctype_be__, big_int)
+            if (hasattr(t, "__ctype_le__")):
+                self.assertRaises(OverflowError, t.__ctype_le__, big_int)
+
 ##    def test_valid_ranges(self):
 ##        # invalid values of the correct type
 ##        # raise ValueError (not OverflowError)
diff -r 7323bced3d48 Modules/_ctypes/cfield.c
--- a/Modules/_ctypes/cfield.c	Sat Apr 16 18:55:16 2011 +0200
+++ b/Modules/_ctypes/cfield.c	Sat Apr 16 18:50:22 2011 -0500
@@ -994,6 +994,19 @@
  * non-integer accessor methods, not supporting bit fields
  */
 
+static void
+float_conversion_error(PyObject *value)
+{
+    if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
+        PyErr_Format(PyExc_OverflowError,
+                     " %s too large to convert to float",
+                     value->ob_type->tp_name);
+    } else {
+        PyErr_Format(PyExc_TypeError,
+                     " float expected instead of %s instance",
+                     value->ob_type->tp_name);
+    }
+}
 
 static PyObject *
 g_set(void *ptr, PyObject *value, Py_ssize_t size)
@@ -1002,9 +1015,7 @@
 
     x = PyFloat_AsDouble(value);
     if (x == -1 && PyErr_Occurred()) {
-        PyErr_Format(PyExc_TypeError,
-                     " float expected instead of %s instance",
-                     value->ob_type->tp_name);
+        float_conversion_error(value);
         return NULL;
     }
     memcpy(ptr, &x, sizeof(long double));
@@ -1026,9 +1037,7 @@
 
     x = PyFloat_AsDouble(value);
     if (x == -1 && PyErr_Occurred()) {
-        PyErr_Format(PyExc_TypeError,
-                     " float expected instead of %s instance",
-                     value->ob_type->tp_name);
+        float_conversion_error(value);
         return NULL;
     }
     memcpy(ptr, &x, sizeof(double));
@@ -1050,9 +1059,7 @@
 
     x = PyFloat_AsDouble(value);
     if (x == -1 && PyErr_Occurred()) {
-        PyErr_Format(PyExc_TypeError,
-                     " float expected instead of %s instance",
-                     value->ob_type->tp_name);
+        float_conversion_error(value);
         return NULL;
     }
 #ifdef WORDS_BIGENDIAN
@@ -1082,9 +1089,7 @@
 
     x = (float)PyFloat_AsDouble(value);
     if (x == -1 && PyErr_Occurred()) {
-        PyErr_Format(PyExc_TypeError,
-                     " float expected instead of %s instance",
-                     value->ob_type->tp_name);
+        float_conversion_error(value);
         return NULL;
     }
     memcpy(ptr, &x, sizeof(x));
@@ -1106,9 +1111,7 @@
 
     x = (float)PyFloat_AsDouble(value);
     if (x == -1 && PyErr_Occurred()) {
-        PyErr_Format(PyExc_TypeError,
-                     " float expected instead of %s instance",
-                     value->ob_type->tp_name);
+        float_conversion_error(value);
         return NULL;
     }
 #ifdef WORDS_BIGENDIAN