diff --git a/core/src/main/java/org/jruby/RubyString.java b/core/src/main/java/org/jruby/RubyString.java
index 0226445d4f2..6bbb16aee80 100644
--- a/core/src/main/java/org/jruby/RubyString.java
+++ b/core/src/main/java/org/jruby/RubyString.java
@@ -5963,8 +5963,11 @@ public IRubyObject encode(ThreadContext context, IRubyObject toEncoding,
 
     @JRubyMethod
     public IRubyObject force_encoding(ThreadContext context, IRubyObject enc) {
+        return force_encoding(context, context.runtime.getEncodingService().getEncodingFromObject(enc));
+    }
+
+    private IRubyObject force_encoding(ThreadContext context, Encoding encoding) {
         modify19();
-        Encoding encoding = context.runtime.getEncodingService().getEncodingFromObject(enc);
         associateEncoding(encoding);
         clearCodeRange();
         return this;
@@ -5982,11 +5985,9 @@ public IRubyObject ascii_only_p(ThreadContext context) {
 
     @JRubyMethod
     public IRubyObject b(ThreadContext context) {
-        Encoding encoding = ASCIIEncoding.INSTANCE;
-        RubyString dup = (RubyString)dup();
-        dup.associateEncoding(encoding);
-        dup.clearCodeRange();
-        return dup;
+        RubyString dup = strDup(context.runtime);
+
+        return dup.force_encoding(context, ASCIIEncoding.INSTANCE);
     }
 
     // MRI: str_scrub arity 0