1 files changed, 22 insertions, 1 deletions
diff --git a/hash.c b/hash.c
index 6ae13ba1b4..c47f21ee9f 100644
--- a/hash.c
+++ b/hash.c
@@ -18,6 +18,7 @@
 #include "probes.h"
 #include "id.h"
 #include "symbol.h"
+#include "gc.h"
 
 #ifdef __APPLE__
 # ifdef HAVE_CRT_EXTERNS_H
@@ -1515,13 +1516,33 @@ hash_aset(st_data_t *key, st_data_t *val, struct update_arg *arg, int existing)
     return ST_CONTINUE;
 }
 
+static VALUE
+fstring_existing_str(VALUE str)
+{
+    st_data_t fstr;
+    st_table *tbl = rb_vm_fstring_table();
+
+    if (st_lookup(tbl, str, &fstr)) {
+	if (rb_objspace_garbage_object_p(fstr)) {
+	    return rb_fstring(str);
+	}
+	else {
+	    return (VALUE)fstr;
+	}
+    }
+    else {
+	return Qnil;
+    }
+}
+
 static int
 hash_aset_str(st_data_t *key, st_data_t *val, struct update_arg *arg, int existing)
 {
     if (!existing && !RB_OBJ_FROZEN(*key)) {
 	VALUE k;
 
-	if ((k = rb_fstring_existing(*key)) != Qnil) {
+	if (!RB_OBJ_TAINTED(*key) &&
+	    (k = fstring_existing_str(*key)) != Qnil) {
 	    *key = k;
 	}
 	else {