diff --git a/dll/win32/setupapi/cfgmgr.c b/dll/win32/setupapi/cfgmgr.c
index fdbcc8cfb1b..b052553e9ac 100644
--- a/dll/win32/setupapi/cfgmgr.c
+++ b/dll/win32/setupapi/cfgmgr.c
@@ -2937,7 +2937,7 @@ CM_Get_Class_Registry_PropertyA(
         *pulLength = WideCharToMultiByte(CP_ACP,
                                          0,
                                          BufferW,
-                                         lstrlenW(BufferW) + 1,
+                                         ulLength,
                                          Buffer,
                                          *pulLength,
                                          NULL,
@@ -3859,7 +3859,7 @@ CM_Get_Device_ID_List_ExA(
     if (WideCharToMultiByte(CP_ACP,
                             0,
                             BufferW,
-                            lstrlenW(BufferW) + 1,
+                            BufferLen,
                             Buffer,
                             BufferLen,
                             NULL,
@@ -4344,7 +4344,7 @@ CM_Get_Device_Interface_List_ExA(
     if (WideCharToMultiByte(CP_ACP,
                             0,
                             BufferW,
-                            lstrlenW(BufferW) + 1,
+                            BufferLen,
                             Buffer,
                             BufferLen,
                             NULL,