diff --git a/AMNet.Server/DllMain.cs b/AMNet.Server/DllMain.cs
index 248ded4..545c713 100644
--- a/AMNet.Server/DllMain.cs
+++ b/AMNet.Server/DllMain.cs
@@ -111,7 +111,7 @@ public static class DllMain
     }
 
     [UnmanagedCallersOnly(EntryPoint = "aime_io_nfc_get_felica_id")]
-    public static int GetFelicaId(byte unitNo, IntPtr idm)
+    public static unsafe int GetFelicaId(byte unitNo, ulong* idm)
     {
         if (!Config.PhysicalCardUseIDm || unitNo != 0)
         {
@@ -123,9 +123,15 @@ public static class DllMain
         {
             return 1;
         }
-     
-        Marshal.Copy(card.IDm, 0, idm, sizeof(ulong));
-        App.Logger.LogInformation("FeliCa IDm read: {idm}", CardPresenter.FormatHexCode(card.IDm));
+
+        ulong idmValue = 0;
+        for (var i = 0 ; i < 8 ; i++) {
+            idmValue = (idmValue << 8) | card.IDm[i];
+        }
+
+        *idm = idmValue;
+
+        App.Logger.LogInformation("FeliCa IDm read: {idm} ({value})", CardPresenter.FormatHexCode(card.IDm), idmValue);
         return 0;
     }