Index: Python/import.c
===================================================================
--- Python/import.c	(revision 80170)
+++ Python/import.c	(working copy)
@@ -2492,8 +2492,24 @@
 		hasit = PyObject_HasAttr(mod, item);
 		if (!hasit) {
 			char *subname = PyString_AS_STRING(item);
+			size_t j, subnamelen = PyString_GET_SIZE(item);
 			PyObject *submod;
 			char *p;
+			/* We must reject an empty name.  As a hack, we bump the
+			   length to 1 so that the loop will balk on the
+			   trailing \0. */
+			if (subnamelen == 0)
+				subnamelen = 1;
+			/* subname must be an identifier */
+			for (j = 0, p = subname; j < subnamelen; j++, p++) {
+				if (!(j == 0 ? isalpha(*p) : isalnum(*p))
+				     && *p != '_') {
+					/* don't raise an exception to stay
+					   backwards compatible */
+					Py_DECREF(item);
+					return 1;
+				}
+			}
 			if (buflen + strlen(subname) >= MAXPATHLEN) {
 				PyErr_SetString(PyExc_ValueError,
 						"Module name too long");