src/java.base/share/classes/sun/nio/cs/ISO_8859_1.java

@@ -130,10 +130,14 @@
             int dp = 0;
             while (dp < len)
                 dst[dp++] = (char)(src[sp++] & 0xff);
             return dp;
         }
+
+        public boolean isASCIICompatible() {
+            return true;
+        }
     }
 
     private static class Encoder extends CharsetEncoder
                                  implements ArrayEncoder {
         private Encoder(Charset cs) {

@@ -295,7 +299,11 @@
                     slen = Math.min((sl - sp), (dst.length - dp));
                 }
             }
             return dp;
         }
+
+        public boolean isASCIICompatible() {
+            return true;
+        }
     }
 }