diff --git a/optimizer/typeinferer.go b/optimizer/typeinferer.go
index e18b030c6a..813396f46e 100644
--- a/optimizer/typeinferer.go
+++ b/optimizer/typeinferer.go
@@ -258,6 +258,10 @@ func (v *typeInferrer) handleFuncCallExpr(x *ast.FuncCallExpr) {
 	switch x.FnName.L {
 	case "abs", "ifnull", "nullif":
 		tp = x.Args[0].GetType()
+		// TODO: We should cover all types.
+		if x.FnName.L == "abs" && tp.Tp == mysql.TypeDatetime {
+			tp = types.NewFieldType(mysql.TypeDouble)
+		}
 	case "pow", "power", "rand":
 		tp = types.NewFieldType(mysql.TypeDouble)
 	case "curdate", "current_date", "date":
diff --git a/optimizer/typeinferer_test.go b/optimizer/typeinferer_test.go
index 8bbd12272b..af044d6d00 100644
--- a/optimizer/typeinferer_test.go
+++ b/optimizer/typeinferer_test.go
@@ -82,6 +82,7 @@ func (ts *testTypeInferrerSuite) TestInferType(c *C) {
 		{"count(c1)", mysql.TypeLonglong, charset.CharsetBin},
 		{"abs(1)", mysql.TypeLonglong, charset.CharsetBin},
 		{"abs(1.1)", mysql.TypeNewDecimal, charset.CharsetBin},
+		{"abs(cast(\"20150817015609\" as DATETIME))", mysql.TypeDouble, charset.CharsetBin},
 		{"IF(1>2,2,3)", mysql.TypeLonglong, charset.CharsetBin},
 		{"IFNULL(1,0)", mysql.TypeLonglong, charset.CharsetBin},
 		{"POW(2,2)", mysql.TypeDouble, charset.CharsetBin},