src/java.base/share/classes/sun/nio/cs/US_ASCII.java

@@ -144,10 +144,14 @@
                 else
                     dst[dp++] = repl;
             }
             return dp;
         }
+
+        public boolean isASCIICompatible() {
+            return true;
+        }
     }
 
     private static class Encoder extends CharsetEncoder
                                  implements ArrayEncoder {
 

@@ -257,8 +261,12 @@
                 }
                 dst[dp++] = repl;
             }
             return dp;
         }
+
+        public boolean isASCIICompatible() {
+            return true;
+        }
     }
 
 }