diff --git a/docs/versionhistory.rst b/docs/versionhistory.rst
index 79a6e200..2d45feb9 100644
--- a/docs/versionhistory.rst
+++ b/docs/versionhistory.rst
@@ -11,6 +11,8 @@ This library adheres to
   regression introduced in v4.4.1)
 - Fixed display of module name for forward references
   (`#492 <https://github.com/agronholm/typeguard/pull/492>`_; PR by @JelleZijlstra)
+- Fixed ``TypeError`` when using an assignment expression
+  (`#510 <https://github.com/agronholm/typeguard/issues/510>`_; PR by @JohannesK71083)
 
 **4.4.1** (2024-11-03)
 
diff --git a/src/typeguard/_transformer.py b/src/typeguard/_transformer.py
index 999dec0c..a9f0aedb 100644
--- a/src/typeguard/_transformer.py
+++ b/src/typeguard/_transformer.py
@@ -1138,8 +1138,20 @@ def visit_NamedExpr(self, node: NamedExpr) -> Any:
                 func_name,
                 [
                     node.value,
-                    Constant(node.target.id),
-                    annotation,
+                    List(
+                        [
+                            List(
+                                [
+                                    Tuple(
+                                        [Constant(node.target.id), annotation],
+                                        ctx=Load(),
+                                    )
+                                ],
+                                ctx=Load(),
+                            )
+                        ],
+                        ctx=Load(),
+                    ),
                     self._memo.get_memo_name(),
                 ],
                 [],
diff --git a/tests/mypy/test_type_annotations.py b/tests/mypy/test_type_annotations.py
index aacee7fb..ac978264 100644
--- a/tests/mypy/test_type_annotations.py
+++ b/tests/mypy/test_type_annotations.py
@@ -31,7 +31,7 @@ def get_negative_mypy_output() -> str:
     )
     output = process.stdout.decode()
     assert output
-    return output
+    return re.sub(r"\n(?!\s|negative\.py)", " ", output.replace("\r", ""))
 
 
 def get_expected_errors() -> Dict[int, str]:
diff --git a/tests/test_transformer.py b/tests/test_transformer.py
index 2e18a5ad..3fb04627 100644
--- a/tests/test_transformer.py
+++ b/tests/test_transformer.py
@@ -1475,7 +1475,7 @@ def foo() -> None:
                 def foo() -> None:
                     memo = TypeCheckMemo(globals(), locals())
                     x: int
-                    if (x := check_variable_assignment(otherfunc(), 'x', int, \
+                    if (x := check_variable_assignment(otherfunc(), [[('x', int)]], \
 memo)):
                         pass
                 """
@@ -1504,7 +1504,7 @@ def foo(x: int) -> None:
                 def foo(x: int) -> None:
                     memo = TypeCheckMemo(globals(), locals())
                     check_argument_types('foo', {'x': (x, int)}, memo)
-                    if (x := check_variable_assignment(otherfunc(), 'x', int, memo)):
+                    if (x := check_variable_assignment(otherfunc(), [[('x', int)]], memo)):
                         pass
                 """
             ).strip()