diff --git a/parse.y b/parse.y
index a7cdddcaec..d76d3b2562 100644
--- a/parse.y
+++ b/parse.y
@@ -9748,7 +9748,7 @@ gettable(struct parser_params *p, ID id, const YYLTYPE *loc)
 	    if (NIL_P(file))
 		file = rb_str_new(0, 0);
 	    else
-		file = rb_str_dup(file);
+		file = rb_str_dup(rb_fstring(file));
 	    node = NEW_STR(add_mark_object(p, file), loc);
 	}
 	return node;
diff --git a/string.c b/string.c
index b37b8542c7..186c71b40c 100644
--- a/string.c
+++ b/string.c
@@ -1162,6 +1162,13 @@ str_replace_shared_without_enc(VALUE str2, VALUE str)
     }
     else {
 	str = rb_str_new_frozen(str);
+        if (!STR_EMBED_P(str2) && !FL_TEST_RAW(str2, STR_SHARED|STR_NOFREE)) {
+            /* TODO: check if str2 is a shared root */
+            char *ptr2 = STR_HEAP_PTR(str2);
+            if (STR_HEAP_PTR(str) != ptr2) {
+                ruby_sized_xfree(ptr2, STR_HEAP_SIZE(str2));
+            }
+        }
 	FL_SET(str2, STR_NOEMBED);
 	RSTRING_GETMEM(str, ptr, len);
 	RSTRING(str2)->as.heap.len = len;