diff --git a/include/ddk/acpiioct.h b/include/ddk/acpiioct.h
index a51cc3dd4b4..d4d550feae1 100644
--- a/include/ddk/acpiioct.h
+++ b/include/ddk/acpiioct.h
@@ -159,7 +159,7 @@ typedef ACPI_ENUM_CHILDREN_OUTPUT_BUFFER UNALIGNED *PACPI_ENUM_CHILDREN_OUTPUT_B
 
 #define ACPI_METHOD_SET_ARGUMENT_STRING( Argument, StrData )                \
     { Argument->Type = ACPI_METHOD_ARGUMENT_STRING;                         \
-      Argument->DataLength = strlen((PUCHAR)StrData) + sizeof(UCHAR);       \
+      Argument->DataLength = strlen((PCHAR)StrData) + sizeof(UCHAR);       \
       RtlCopyMemory(&Argument->Data[0],(PUCHAR)StrData,Argument->DataLength); }
 
 #define ACPI_METHOD_SET_ARGUMENT_BUFFER( Argument, BuffData, BuffLength )   \