Index: Lib/test/test_math.py
===================================================================
--- Lib/test/test_math.py	(revision 66056)
+++ Lib/test/test_math.py	(working copy)
@@ -511,6 +511,9 @@
         self.ftest('log(32,2)', math.log(32,2), 5)
         self.ftest('log(10**40, 10)', math.log(10**40, 10), 40)
         self.ftest('log(10**40, 10**20)', math.log(10**40, 10**20), 2)
+        self.ftest('log(1000, 10)', math.log(1000, 10), 3)
+        self.ftest('log(1000, 10.0)', math.log(1000, 10.0), 3)
+        self.ftest('log(1000, 10L)', math.log(1000, 10L), 3)
         self.assertEquals(math.log(INF), INF)
         self.assertRaises(ValueError, math.log, NINF)
         self.assert_(math.isnan(math.log(NAN)))
Index: Modules/mathmodule.c
===================================================================
--- Modules/mathmodule.c	(revision 66056)
+++ Modules/mathmodule.c	(working copy)
@@ -762,6 +762,30 @@
 	if (num == NULL || base == NULL)
 		return num;
 
+	/* Use log10 when called with 10 as base to increase accuracy
+	   and performance. */
+	if (PyInt_Check(base)) {
+		if (PyInt_AsLong(base) == 10) {
+				return loghelper(arg, log10, "log");
+		}
+		else
+			PyErr_Clear();
+	}
+	else if (PyLong_Check(base)) {
+		if (PyLong_AsLong(base) == 10) {
+				return loghelper(arg, log10, "log");
+			}
+			else
+				PyErr_Clear();
+	}
+	else if (PyFloat_Check(base)) {
+		 if (PyFloat_AsDouble(base) == 10.0) {
+				return loghelper(arg, log10, "log");
+		}
+		else
+			PyErr_Clear();
+	}
+
 	den = loghelper(base, log, "log");
 	if (den == NULL) {
 		Py_DECREF(num);