diff --git a/hash.c b/hash.c
index 78e9d9a2d6..b15d856ee1 100644
--- a/hash.c
+++ b/hash.c
@@ -1557,7 +1557,15 @@ hash_copy(VALUE ret, VALUE hash)
 static VALUE
 hash_dup_with_compare_by_id(VALUE hash)
 {
-    return hash_copy(copy_compare_by_id(rb_hash_new(), hash), hash);
+    VALUE dup = hash_alloc_flags(rb_cHash, 0, Qnil, RHASH_ST_TABLE_P(hash));
+    if (RHASH_ST_TABLE_P(hash)) {
+        RHASH_SET_ST_FLAG(dup);
+    }
+    else {
+        RHASH_UNSET_ST_FLAG(dup);
+    }
+
+    return hash_copy(dup, hash);
 }
 
 static VALUE
diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index 70daea0ef1..c72b256bab 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -1458,6 +1458,16 @@ class TestHash < Test::Unit::TestCase
     assert_predicate(h.dup, :compare_by_identity?, bug8703)
   end
 
+  def test_compare_by_identy_memory_leak
+    assert_no_memory_leak([], "", "#{<<~"begin;"}\n#{<<~'end;'}", "[Bug #20145]", rss: true)
+    begin;
+      h = { 1 => 2 }.compare_by_identity
+      1_000_000.times do
+        h.select { false }
+      end
+    end;
+  end
+
   def test_same_key
     bug9646 = '[ruby-dev:48047] [Bug #9646] Infinite loop at Hash#each'
     h = @cls[a=[], 1]
diff --git a/version.h b/version.h
index fe3b13e59c..e8ee7a320a 100644
--- a/version.h
+++ b/version.h
@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 0
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 4
+#define RUBY_PATCHLEVEL 5
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"