diff --git a/CHANGES.rst b/CHANGES.rst
index eab7aa72e..473b9d3b1 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -14,6 +14,24 @@ Changelog
 
 .. towncrier release notes start
 
+6.6.3
+=====
+
+*(2025-06-30)*
+
+
+Bug fixes
+---------
+
+- Fixed inconsistencies generated by the C implementation of ``_md_shrink()`` which might later lead to assertion failures and crash -- by :user:`Romain-Geissler-1A`.
+
+  *Related issues and pull requests on GitHub:*
+  :issue:`1229`.
+
+
+----
+
+
 6.6.2
 =====
 
diff --git a/CHANGES/1229.bugfix.rst b/CHANGES/1229.bugfix.rst
deleted file mode 100644
index a8ba7a4a7..000000000
--- a/CHANGES/1229.bugfix.rst
+++ /dev/null
@@ -1 +0,0 @@
-Fixed inconsistencies generated by the C implementation of ``_md_shrink()`` which might later lead to assertion failures and crash -- by :user:`Romain-Geissler-1A`.
diff --git a/multidict/__init__.py b/multidict/__init__.py
index 841264659..c506324f3 100644
--- a/multidict/__init__.py
+++ b/multidict/__init__.py
@@ -22,7 +22,7 @@
     "getversion",
 )
 
-__version__ = "6.6.2"
+__version__ = "6.6.3"
 
 
 if TYPE_CHECKING or not USE_EXTENSIONS:
diff --git a/setup.py b/setup.py
index 73b070d02..318229fcc 100644
--- a/setup.py
+++ b/setup.py
@@ -10,7 +10,7 @@
 if sys.implementation.name != "cpython":
     NO_EXTENSIONS = True
 
-CFLAGS = ["-O0", "-g3", "-UNDEBUG"] if DEBUG_BUILD else ["-O3"]
+CFLAGS = ["-O0", "-g3", "-UNDEBUG"] if DEBUG_BUILD else ["-O3", "-DNDEBUG"]
 
 if platform.system() != "Windows":
     CFLAGS.extend(