diff --git a/api.go b/api.go
index 4a8605856f..8772994e47 100644
--- a/api.go
+++ b/api.go
@@ -555,8 +555,10 @@ func postContainersStart(srv *Server, version float64, w http.ResponseWriter, r
 
 	// allow a nil body for backwards compatibility
 	if r.Body != nil {
-		if err := json.NewDecoder(r.Body).Decode(hostConfig); err != nil {
-			return err
+		if r.Header.Get("Content-Type") == "application/json" {
+			if err := json.NewDecoder(r.Body).Decode(hostConfig); err != nil {
+				return err
+			}
 		}
 	}