diff --git a/vapi/glib-2.0.vapi b/vapi/glib-2.0.vapi
index 596570a..ab680a9 100644
--- a/vapi/glib-2.0.vapi
+++ b/vapi/glib-2.0.vapi
@@ -1129,7 +1129,7 @@ public class string {
 		if (str == null) {
 			str_size = 0;
 		} else {
-			str_size = str.size ();
+			str_size = ((string)str).size ();
 		}
 
 		string* result = GLib.malloc0 (this.size () - ((char*) end_string - (char*) start_string) + str_size + 1);
@@ -2693,12 +2693,12 @@ namespace GLib {
 				if (c == '\n') {
 					break;
 				}
-				ret.append_c ((char) c);
+				((StringBuilder)ret).append_c ((char) c);
 			}
 			if (ret == null) {
 				return null;
 			} else {
-				return ret.str;
+				return ((StringBuilder)ret).str;
 			}
 		}
 	}