diff --git a/voicevox_engine/synthesis_engine/core_wrapper.py b/voicevox_engine/synthesis_engine/core_wrapper.py
index 14afa427f..dcb2da101 100644
--- a/voicevox_engine/synthesis_engine/core_wrapper.py
+++ b/voicevox_engine/synthesis_engine/core_wrapper.py
@@ -378,6 +378,64 @@ def load_core(core_dir: Path, use_gpu: bool) -> CDLL:
         raise RuntimeError(f"このコンピュータのアーキテクチャ {platform.machine()} で利用可能なコアがありません")
 
 
+def _type_yukarin_s_forward(core_cdll: CDLL) -> None:
+    """
+    コアDLL `yukarin_s_forward` 関数の型付け
+    Parameters
+    ----------
+    core_cdll : CDLL
+        コアDLL
+    """
+    core_cdll.yukarin_s_forward.argtypes = (
+        c_int,
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_float),
+    )
+    core_cdll.yukarin_s_forward.restype = c_bool
+
+
+def _type_yukarin_sa_forward(core_cdll: CDLL) -> None:
+    """
+    コアDLL `yukarin_sa_forward` 関数の型付け
+    Parameters
+    ----------
+    core_cdll : CDLL
+        コアDLL
+    """
+    core_cdll.yukarin_sa_forward.argtypes = (
+        c_int,
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_long),
+        POINTER(c_float),
+    )
+    core_cdll.yukarin_sa_forward.restype = c_bool
+
+
+def _type_decode_forward(core_cdll: CDLL) -> None:
+    """
+    コアDLL `decode_forward` 関数の型付け
+    Parameters
+    ----------
+    core_cdll : CDLL
+        コアDLL
+    """
+    core_cdll.decode_forward.argtypes = (
+        c_int,
+        c_int,
+        POINTER(c_float),
+        POINTER(c_float),
+        POINTER(c_long),
+        POINTER(c_float),
+    )
+    core_cdll.decode_forward.restype = c_bool
+
+
 class CoreWrapper:
     def __init__(
         self,
@@ -393,9 +451,9 @@ def __init__(
 
         self.core.initialize.restype = c_bool
         self.core.metas.restype = c_char_p
-        self.core.yukarin_s_forward.restype = c_bool
-        self.core.yukarin_sa_forward.restype = c_bool
-        self.core.decode_forward.restype = c_bool
+        _type_yukarin_s_forward(self.core)
+        _type_yukarin_sa_forward(self.core)
+        _type_decode_forward(self.core)
         self.core.last_error_message.restype = c_char_p
 
         self.exist_supported_devices = False
@@ -426,32 +484,6 @@ def __init__(
             self.exist_finalize = True
             exist_cpu_num_threads = True
 
-        self.core.yukarin_s_forward.argtypes = (
-            c_int,
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_float),
-        )
-        self.core.yukarin_sa_forward.argtypes = (
-            c_int,
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_long),
-            POINTER(c_float),
-        )
-        self.core.decode_forward.argtypes = (
-            c_int,
-            c_int,
-            POINTER(c_float),
-            POINTER(c_float),
-            POINTER(c_long),
-            POINTER(c_float),
-        )
-
         cwd = os.getcwd()
         os.chdir(core_dir)
         try: