diff --git a/windows.c b/windows.c
index 644a701..360da73 100644
--- a/windows.c
+++ b/windows.c
@@ -30,12 +30,13 @@ static void enumerate_hub(struct sp_port *port, const char *hub_name,
 
 static char *wc_to_utf8(PWCHAR wc_buffer, ULONG size)
 {
-       WCHAR wc_str[(size / sizeof(WCHAR)) + 1];
+       ULONG wc_length = size / sizeof(WCHAR);
+       WCHAR wc_str[wc_length + 1];
        char *utf8_str;
 
        /* Zero-terminate the wide char string. */
        memcpy(wc_str, wc_buffer, size);
-       wc_str[sizeof(wc_str) - 1] = 0;
+       wc_str[wc_length] = 0;
 
        /* Compute the size of the UTF-8 converted string. */
        if (!(size = WideCharToMultiByte(CP_ACP, WC_NO_BEST_FIT_CHARS, wc_str, -1,