diff --git a/core/src/main/java/org/jruby/RubyInteger.java b/core/src/main/java/org/jruby/RubyInteger.java
index df87603652a8..44c7b4442062 100644
--- a/core/src/main/java/org/jruby/RubyInteger.java
+++ b/core/src/main/java/org/jruby/RubyInteger.java
@@ -441,7 +441,7 @@ public static ByteList singleCharUTF8ByteList(final byte index) {
      */
     public static RubyString singleCharString(Ruby runtime, byte b, RubyClass meta, Encoding enc) {
         ByteList bytes;
-        if (enc == USASCIIEncoding.INSTANCE) {
+        if (enc.isAsciiCompatible()) {
             bytes = singleCharByteList(b);
         } else if (Byte.toUnsignedInt(b) < 0x80 && enc == RubyString.UTF8) {
             bytes = singleCharUTF8ByteList(b);