diff --git a/hash.c b/hash.c
index dd269d194e..a1fedb84a3 100644
--- a/hash.c
+++ b/hash.c
@@ -3968,19 +3968,10 @@ rb_hash_invert(VALUE hash)
     return h;
 }
 
-static int
-rb_hash_update_callback(st_data_t *key, st_data_t *value, struct update_arg *arg, int existing)
-{
-    *value = arg->arg;
-    return ST_CONTINUE;
-}
-
-NOINSERT_UPDATE_CALLBACK(rb_hash_update_callback)
-
 static int
 rb_hash_update_i(VALUE key, VALUE value, VALUE hash)
 {
-    RHASH_UPDATE(hash, key, rb_hash_update_callback, value);
+    rb_hash_aset(hash, key, value);
     return ST_CONTINUE;
 }
 
@@ -3992,6 +3983,9 @@ rb_hash_update_block_callback(st_data_t *key, st_data_t *value, struct update_ar
     if (existing) {
         newvalue = (st_data_t)rb_yield_values(3, (VALUE)*key, (VALUE)*value, (VALUE)newvalue);
     }
+    else if (RHASH_STRING_KEY_P(arg->hash, *key) && !RB_OBJ_FROZEN(*key)) {
+        *key = rb_hash_key_str(*key);
+    }
     *value = newvalue;
     return ST_CONTINUE;
 }
diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index 639c0105c0..cef9f88a3c 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -1397,6 +1397,15 @@ class TestHash < Test::Unit::TestCase
     assert_equal(@cls[a: 10, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10], h)
   end
 
+  def test_update_on_identhash
+    key = +'a'
+    i = @cls[].compare_by_identity
+    i[key] = 0
+    h = @cls[].update(i)
+    key.upcase!
+    assert_equal(0, h.fetch('a'))
+  end
+
   def test_merge
     h1 = @cls[1=>2, 3=>4]
     h2 = {1=>3, 5=>7}
@@ -1419,10 +1428,10 @@ class TestHash < Test::Unit::TestCase
     expected[7] = 8
     h2 = h.merge(7=>8)
     assert_equal(expected, h2)
-    assert_equal(true, h2.compare_by_identity?)
+    assert_predicate(h2, :compare_by_identity?)
     h2 = h.merge({})
     assert_equal(h, h2)
-    assert_equal(true, h2.compare_by_identity?)
+    assert_predicate(h2, :compare_by_identity?)
 
     h = @cls[]
     h.compare_by_identity
@@ -1430,10 +1439,10 @@ class TestHash < Test::Unit::TestCase
     h1.compare_by_identity
     h2 = h.merge(7=>8)
     assert_equal(h1, h2)
-    assert_equal(true, h2.compare_by_identity?)
+    assert_predicate(h2, :compare_by_identity?)
     h2 = h.merge({})
     assert_equal(h, h2)
-    assert_equal(true, h2.compare_by_identity?)
+    assert_predicate(h2, :compare_by_identity?)
   end
 
   def test_merge!
diff --git a/version.h b/version.h
index ffb9b1c250..71e4b15dd7 100644
--- a/version.h
+++ b/version.h
@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 4
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 186
+#define RUBY_PATCHLEVEL 187
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"