--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java	Tue Dec 19 13:58:31 2017 -0800
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java	Wed Dec 20 15:33:31 2017 +0000
@@ -1976,8 +1976,8 @@
                          types.covariantReturnType(rt2, rt1, types.noWarnings)) ||
                          checkCommonOverriderIn(s1,s2,site);
                     if (!compat) {
-                        log.error(pos, Errors.TypesIncompatibleDiffRet(t1, t2, s2.name +
-                                "(" + types.memberType(t2, s2).getParameterTypes() + ")"));
+                        log.error(pos, Errors.TypesIncompatible(t1, t2,
+                                Fragments.IncompatibleDiffRet(s2.name, types.memberType(t2, s2).getParameterTypes())));
                         return s2;
                     }
                 } else if (checkNameClash((ClassSymbol)site.tsym, s1, s2) &&
@@ -2563,20 +2563,22 @@
                         //strong semantics - issue an error if two sibling interfaces
                         //have two override-equivalent defaults - or if one is abstract
                         //and the other is default
-                        String errKey;
+                        Fragment diagKey;
                         Symbol s1 = defaults.first();
                         Symbol s2;
                         if (defaults.size() > 1) {
-                            errKey = "types.incompatible.unrelated.defaults";
                             s2 = defaults.toList().tail.head;
+                            diagKey = Fragments.IncompatibleUnrelatedDefaults(Kinds.kindName(site.tsym), site,
+                                    m.name, types.memberType(site, m).getParameterTypes(),
+                                    s1.location(), s2.location());
+
                         } else {
-                            errKey = "types.incompatible.abstract.default";
                             s2 = abstracts.first();
+                            diagKey = Fragments.IncompatibleAbstractDefault(Kinds.kindName(site.tsym), site,
+                                    m.name, types.memberType(site, m).getParameterTypes(),
+                                    s1.location(), s2.location());
                         }
-                        log.error(pos, errKey,
-                                Kinds.kindName(site.tsym), site,
-                                m.name, types.memberType(site, m).getParameterTypes(),
-                                s1.location(), s2.location());
+                        log.error(pos, Errors.TypesIncompatible(s1.location().type, s2.location().type, diagKey));
                         break;
                     }
                 }