diff --git a/pack.c b/pack.c
index 1fbbd724d7..7de07a51d1 100644
--- a/pack.c
+++ b/pack.c
@@ -212,12 +212,13 @@ pack_pack(rb_execution_context_t *ec, VALUE ary, VALUE fmt, VALUE buffer)
     pend = p + RSTRING_LEN(fmt);
 
     if (NIL_P(buffer)) {
-	res = rb_str_buf_new(0);
+        res = rb_str_buf_new(0);
     }
     else {
         if (!RB_TYPE_P(buffer, T_STRING))
             rb_raise(rb_eTypeError, "buffer must be String, not %s", rb_obj_classname(buffer));
-	res = buffer;
+        rb_str_modify(buffer);
+        res = buffer;
     }
 
     idx = 0;
diff --git a/test/ruby/test_array.rb b/test/ruby/test_array.rb
index a97a9c2558..ccbe85877f 100644
--- a/test/ruby/test_array.rb
+++ b/test/ruby/test_array.rb
@@ -1294,6 +1294,12 @@ class TestArray < Test::Unit::TestCase
 =end
   end
 
+  def test_pack_with_buffer
+    n = [ 65, 66, 67 ]
+    str = "a" * 100
+    assert_equal("aaaABC", n.pack("@3ccc", buffer: str.dup), "[Bug #19116]")
+  end
+
   def test_pop
     a = @cls[ 'cat', 'dog' ]
     assert_equal('dog', a.pop)
diff --git a/version.h b/version.h
index 043cd33b38..8a59f3ea0d 100644
--- a/version.h
+++ b/version.h
@@ -11,11 +11,11 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 3
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 177
+#define RUBY_PATCHLEVEL 178
 
 #define RUBY_RELEASE_YEAR 2022
 #define RUBY_RELEASE_MONTH 11
-#define RUBY_RELEASE_DAY 5
+#define RUBY_RELEASE_DAY 13
 
 #include "ruby/version.h"