diff -r a32a3b79f5e8 Misc/ACKS
--- a/Misc/ACKS	Sun May 12 17:29:34 2013 +0300
+++ b/Misc/ACKS	Wed May 15 11:46:45 2013 +0300
@@ -693,6 +693,7 @@
 Dom Mitchell
 Florian Mladitsch
 Doug Moen
+Jaakko Moisio
 The Dragon De Monsyne
 Skip Montanaro
 Paul Moore
diff -r a32a3b79f5e8 Misc/NEWS
--- a/Misc/NEWS	Sun May 12 17:29:34 2013 +0300
+++ b/Misc/NEWS	Wed May 15 11:46:45 2013 +0300
@@ -35,6 +35,9 @@
 
 - Issue #17610: Don't rely on non-standard behavior of the C qsort() function.
 
+- Issue #17976: Fixed potential problem with file_write not detecting IO error
+  by inspecting the return value of fwrite.
+
 Library
 -------
 
diff -r a32a3b79f5e8 Objects/fileobject.c
--- a/Objects/fileobject.c	Sun May 12 17:29:34 2013 +0300
+++ b/Objects/fileobject.c	Wed May 15 11:46:45 2013 +0300
@@ -1804,6 +1804,7 @@
     const char *s;
     Py_ssize_t n, n2;
     PyObject *encoded = NULL;
+    int err_flag = 0, err;
 
     if (f->f_fp == NULL)
         return err_closed();
@@ -1849,11 +1850,16 @@
     FILE_BEGIN_ALLOW_THREADS(f)
     errno = 0;
     n2 = fwrite(s, 1, n, f->f_fp);
+    if (n2 != n || ferror(f->f_fp)) {
+        err_flag = 1;
+        err = errno;
+    }
     FILE_END_ALLOW_THREADS(f)
     Py_XDECREF(encoded);
     if (f->f_binary)
         PyBuffer_Release(&pbuf);
-    if (n2 != n) {
+    if (err_flag) {
+        errno = err;
         PyErr_SetFromErrno(PyExc_IOError);
         clearerr(f->f_fp);
         return NULL;