1 files changed, 3 insertions, 1 deletions
diff --git a/string.c b/string.c
index 4f27d431ff..f0cea48267 100644
--- a/string.c
+++ b/string.c
@@ -775,7 +775,9 @@ VALUE
 rb_str_buf_append(str, str2)
     VALUE str, str2;
 {
-    return str_buf_cat(str, RSTRING(str2)->ptr, RSTRING(str2)->len);
+    str_buf_cat(str, RSTRING(str2)->ptr, RSTRING(str2)->len);
+    OBJ_INFECT(str, str2);
+    return str;
 }
 
 VALUE