diff --git a/CHANGES.txt b/CHANGES.txt
index c59259a953fb..f5afcdf47c5c 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,10 @@
   Python
   * Make libprotobuf symbols local on OSX to fix issue #9395 (#9435)
 
+  Ruby
+  * Fixed a data loss bug that could occur when the number of `optional`
+    fields in a message is an exact multiple of 32. (#9440).
+
 2022-01-10 version 3.19.3 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
 
   Python
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.c b/ruby/ext/google/protobuf_c/ruby-upb.c
index d68caac0e2cc..d6c2a0bc5d3e 100755
--- a/ruby/ext/google/protobuf_c/ruby-upb.c
+++ b/ruby/ext/google/protobuf_c/ruby-upb.c
@@ -5583,7 +5583,7 @@ static void make_layout(symtab_addctx *ctx, const upb_msgdef *m) {
   }
 
   /* Account for space used by hasbits. */
-  l->size = div_round_up(hasbit, 8);
+  l->size = div_round_up(hasbit + 1, 8);
 
   /* Allocate non-oneof fields. */
   for (upb_msg_field_begin(&it, m); !upb_msg_field_done(&it);
diff --git a/ruby/tests/basic.rb b/ruby/tests/basic.rb
index 841b8b502f22..b9d1554dbd33 100755
--- a/ruby/tests/basic.rb
+++ b/ruby/tests/basic.rb
@@ -71,6 +71,14 @@ def test_issue_8559_crash
       TestMessage.encode(msg)
     end
 
+    def test_issue_9440
+      msg = HelloRequest.new
+      msg.id = 8
+      assert_equal 8, msg.id
+      msg.version = '1'
+      assert_equal 8, msg.id
+    end
+
     def test_has_field
       m = TestSingularFields.new
       assert !m.has_singular_msg?
diff --git a/ruby/tests/basic_test.proto b/ruby/tests/basic_test.proto
index bca172a722ec..fb70f479db5b 100644
--- a/ruby/tests/basic_test.proto
+++ b/ruby/tests/basic_test.proto
@@ -215,3 +215,38 @@ message WithJsonName {
   optional int32 foo_bar = 1 [json_name="jsonFooBar"];
   repeated WithJsonName baz = 2 [json_name="jsonBaz"];
 }
+
+message HelloRequest {
+  optional uint32 id = 1;
+  optional uint32 random_name_a0 = 2;
+  optional uint32 random_name_a1 = 3;
+  optional uint32 random_name_a2 = 4;
+  optional uint32 random_name_a3 = 5;
+  optional uint32 random_name_a4 = 6;
+  optional uint32 random_name_a5 = 7;
+  optional uint32 random_name_a6 = 8;
+  optional uint32 random_name_a7 = 9;
+  optional uint32 random_name_a8 = 10;
+  optional uint32 random_name_a9 = 11;
+  optional uint32 random_name_b0 = 12;
+  optional uint32 random_name_b1 = 13;
+  optional uint32 random_name_b2 = 14;
+  optional uint32 random_name_b3 = 15;
+  optional uint32 random_name_b4 = 16;
+  optional uint32 random_name_b5 = 17;
+  optional uint32 random_name_b6 = 18;
+  optional uint32 random_name_b7 = 19;
+  optional uint32 random_name_b8 = 20;
+  optional uint32 random_name_b9 = 21;
+  optional uint32 random_name_c0 = 22;
+  optional uint32 random_name_c1 = 23;
+  optional uint32 random_name_c2 = 24;
+  optional uint32 random_name_c3 = 25;
+  optional uint32 random_name_c4 = 26;
+  optional uint32 random_name_c5 = 27;
+  optional uint32 random_name_c6 = 28;
+  optional uint32 random_name_c7 = 29;
+  optional uint32 random_name_c8 = 30;
+  optional uint32 random_name_c9 = 31;
+  optional string version = 32;
+}