diff --git a/src/main.c b/src/main.c
index 3f6f048..55a7aea 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1299,15 +1299,15 @@ getopt_configured(int argc, char * const argv[], const char *optstring,
 static int
 getopt_lengh_unit(const char *optarg, double *input_div, gerbv_screen_t *screen)
 {
-	if (strncasecmp(optarg, "mm", 2) == 0) {
+	if (g_ascii_strncasecmp(optarg, "mm", 2) == 0) {
 		*input_div = 25.4;
 		screen->unit = GERBV_MMS;
 		screen->unit_is_from_cmdline = TRUE;
-	} else if (strncasecmp(optarg, "mil", 3) == 0) {
+	} else if (g_ascii_strncasecmp(optarg, "mil", 3) == 0) {
 		*input_div = 1000.0;
 		screen->unit = GERBV_MILS;
 		screen->unit_is_from_cmdline = TRUE;
-	} else if (strncasecmp(optarg, "inch", 4) == 0) {
+	} else if (g_ascii_strncasecmp(optarg, "inch", 4) == 0) {
 		*input_div = 1.0;
 		screen->unit = GERBV_INS;
 		screen->unit_is_from_cmdline = TRUE;