diff -r e392f1b88fff Lib/test/test_marshal.py
--- a/Lib/test/test_marshal.py	Mon May 20 10:28:48 2013 -0700
+++ b/Lib/test/test_marshal.py	Mon May 20 23:27:33 2013 +0300
@@ -2,6 +2,7 @@
 
 from test import support
 import array
+import io
 import marshal
 import sys
 import unittest
@@ -264,6 +265,17 @@
         for i in range(len(data)):
             self.assertRaises(EOFError, marshal.loads, data[0: i])
 
+    def test_bad_reader(self):
+        class BadReader(io.BytesIO):
+            def read(self, n=-1):
+                b = super().read(n)
+                if n is not None and n > 4:
+                    b += b' ' * 10**6
+                return b
+        for value in (1.0, 1j, b'0123456789', '0123456789'):
+            self.assertRaises(ValueError, marshal.load,
+                              BadReader(marshal.dumps(value)))
+
 LARGE_SIZE = 2**31
 pointer_size = 8 if sys.maxsize > 0xFFFFFFFF else 4
 
diff -r e392f1b88fff Python/marshal.c
--- a/Python/marshal.c	Mon May 20 10:28:48 2013 -0700
+++ b/Python/marshal.c	Mon May 20 23:27:33 2013 +0300
@@ -569,10 +569,19 @@
                              data->ob_type->tp_name);
             }
             else {
-                read = (int)PyBytes_GET_SIZE(data);
+                read = PyBytes_GET_SIZE(data);
                 if (read > 0) {
-                    ptr = PyBytes_AS_STRING(data);
-                    memcpy(s, ptr, read);
+                    if (read > n) {
+                        PyErr_Format(PyExc_ValueError,
+                                    "read() returned too much data: "
+                                    "%zd bytes requested, %zd returned",
+                                    n, read);
+                        read = -1;
+                    }
+                    else {
+                        ptr = PyBytes_AS_STRING(data);
+                        memcpy(s, ptr, read);
+                    }
                 }
             }
             Py_DECREF(data);
@@ -842,11 +851,13 @@
             double dx;
             retval = NULL;
             n = r_byte(p);
-            if (n == EOF || r_string(buf, n, p) != n) {
+            if (n == EOF) {
                 PyErr_SetString(PyExc_EOFError,
                     "EOF read where object expected");
                 break;
             }
+            if (r_string(buf, n, p) != n)
+                break;
             buf[n] = '\0';
             dx = PyOS_string_to_double(buf, NULL, NULL);
             if (dx == -1.0 && PyErr_Occurred())
@@ -861,8 +872,6 @@
             unsigned char buf[8];
             double x;
             if (r_string((char*)buf, 8, p) != 8) {
-                PyErr_SetString(PyExc_EOFError,
-                    "EOF read where object expected");
                 retval = NULL;
                 break;
             }
@@ -882,21 +891,25 @@
             Py_complex c;
             retval = NULL;
             n = r_byte(p);
-            if (n == EOF || r_string(buf, n, p) != n) {
+            if (n == EOF) {
                 PyErr_SetString(PyExc_EOFError,
                     "EOF read where object expected");
                 break;
             }
+            if (r_string(buf, n, p) != n)
+                break;
             buf[n] = '\0';
             c.real = PyOS_string_to_double(buf, NULL, NULL);
             if (c.real == -1.0 && PyErr_Occurred())
                 break;
             n = r_byte(p);
-            if (n == EOF || r_string(buf, n, p) != n) {
+            if (n == EOF) {
                 PyErr_SetString(PyExc_EOFError,
                     "EOF read where object expected");
                 break;
             }
+            if (r_string(buf, n, p) != n)
+                break;
             buf[n] = '\0';
             c.imag = PyOS_string_to_double(buf, NULL, NULL);
             if (c.imag == -1.0 && PyErr_Occurred())
@@ -911,8 +924,6 @@
             unsigned char buf[8];
             Py_complex c;
             if (r_string((char*)buf, 8, p) != 8) {
-                PyErr_SetString(PyExc_EOFError,
-                    "EOF read where object expected");
                 retval = NULL;
                 break;
             }
@@ -922,8 +933,6 @@
                 break;
             }
             if (r_string((char*)buf, 8, p) != 8) {
-                PyErr_SetString(PyExc_EOFError,
-                    "EOF read where object expected");
                 retval = NULL;
                 break;
             }
@@ -955,8 +964,6 @@
         }
         if (r_string(PyBytes_AS_STRING(v), n, p) != n) {
             Py_DECREF(v);
-            PyErr_SetString(PyExc_EOFError,
-                            "EOF read where object expected");
             retval = NULL;
             break;
         }
@@ -986,8 +993,6 @@
         }
         if (r_string(buffer, n, p) != n) {
             PyMem_DEL(buffer);
-            PyErr_SetString(PyExc_EOFError,
-                "EOF read where object expected");
             retval = NULL;
             break;
         }