1 files changed, 17 insertions, 1 deletions
diff --git a/string.c b/string.c
index f5e089aa21..d9b5278eb6 100644
--- a/string.c
+++ b/string.c
@@ -10779,7 +10779,23 @@ rb_str_b(VALUE str)
         str2 = str_alloc_embed(rb_cString, RSTRING_EMBED_LEN(str) + TERM_LEN(str));
     }
     str_replace_shared_without_enc(str2, str);
-    ENC_CODERANGE_CLEAR(str2);
+
+    // BINARY strings can never be broken; they're either 7-bit ASCII or VALID.
+    // If we know the receiver's code range then we know the result's code range.
+    int cr = ENC_CODERANGE(str);
+    switch (cr) {
+        case ENC_CODERANGE_7BIT:
+            ENC_CODERANGE_SET(str2, ENC_CODERANGE_7BIT);
+            break;
+        case ENC_CODERANGE_BROKEN:
+        case ENC_CODERANGE_VALID:
+            ENC_CODERANGE_SET(str2, ENC_CODERANGE_VALID);
+            break;
+        default:
+            ENC_CODERANGE_CLEAR(str2);
+            break;
+    }
+
     return str2;
 }