Castillo will start Sunday's game against the Twins, Daniel Kramer of MLB.com reports.
Castillo was initially projected to start Tuesday at Baltimore but with Bryan Woo (hamstring) hitting the IL, Castillo will pitch Sunday on regular rest. The 31-year-old has surrendered four or more runs in three of his last four starts but owns a 3.79 ERA over 99.2 innings on the year.