diff --git a/string.c b/string.c
index 386c460740..895fe62952 100644
--- a/string.c
+++ b/string.c
@@ -1505,9 +1505,14 @@ str_duplicate(VALUE klass, VALUE str)
 	   char, embed_size);
     if (flags & STR_NOEMBED) {
 	if (UNLIKELY(!(flags & FL_FREEZE))) {
-	    str = str_new_frozen(klass, str);
-	    FL_SET_RAW(str, flags & FL_TAINT);
-	    flags = FL_TEST_RAW(str, flag_mask);
+            if (FL_TEST_RAW(str, STR_SHARED)) {
+                str = RSTRING(str)->as.heap.aux.shared;
+            }
+            else {
+                str = str_new_frozen(klass, str);
+                FL_SET_RAW(str, flags & FL_TAINT);
+                flags = FL_TEST_RAW(str, flag_mask);
+            }
 	}
 	if (flags & STR_NOEMBED) {
 	    RB_OBJ_WRITE(dup, &RSTRING(dup)->as.heap.aux.shared, str);
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index d94c4da7ae..f591f7ea9d 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -2961,6 +2961,15 @@ CODE
   end
 =end
 
+  def test_nesting_shared
+    a = ('a' * 24).encode(Encoding::ASCII).gsub('x', '')
+    hash = {}
+    hash[a] = true
+    assert_equal(('a' * 24), a)
+    4.times { GC.start }
+    assert_equal(('a' * 24), a, '[Bug #15792]')
+  end
+
   def test_shared_force_encoding
     s = "\u{3066}\u{3059}\u{3068}".gsub(//, '')
     h = {}