Standard & Poor's raised its mortgage servicer rating for a subsidiary of Walter Investment Management Corp. (WAC), the company said Friday. Analysts boosted the residential special servicer ranking for Green Tree to above average, according to S&P. The ratings agency also affirmed Green Tree's above average status in subprime, subordinate-lien and asset-backed manufactured housing servicing. Standard & Poor's raised its mortgage servicer rating for a subsidiary of Walter Investment Management Corp. (WAC), the company said Friday. Analysts boosted the residential special servicer ranking for Green Tree to above average, according to S&P. The ratings agency also affirmed Green Tree's above average status in subprime, subordinate-lien and asset-backed manufactured housing servicing. Tampa, Fla.-based Walter Investment acquired Green Tree, a special servicer, in July for about $1.07 billion. "We view the ranking assigned by Standard & Poor's to be extremely positive," Walter Investment Chairman and CEO Mark O'Brien said in a release. Fitch Ratings affirmed Green Tree's special servicer rating at RSS2+ in early December. Fitch rates servicers on a scale of 1 to 5, with the lower number indicative of the highest ratings. In October, Walter Investment expanded its mortgage-servicing portfolio to $59 billion, a 76% increase in the previous two quarters according to FBR Capital Markets. Write to Andrew Scoggin. Follow him on Twitter @ascoggin.