1 files changed, 3 insertions, 0 deletions
diff --git a/string.c b/string.c
index 030465235a..8ac33e3e52 100644
--- a/string.c
+++ b/string.c
@@ -321,6 +321,9 @@ rb_fstring(VALUE str)
 	return str;
     }
 
+    if (!OBJ_FROZEN(str))
+        rb_str_resize(str, RSTRING_LEN(str));
+
     fstr = register_fstring(str);
 
     if (!bare) {