diff --git a/tests/driver_isl29125/main.c b/tests/driver_isl29125/main.c
index d75dc0cafe8beda60c0eceab8fd0e8d137898967..a3e3cb388d8d1a131fc04744dbedcd5e10d4a467 100644
--- a/tests/driver_isl29125/main.c
+++ b/tests/driver_isl29125/main.c
@@ -76,7 +76,7 @@ int main(void)
         "ISL29125_MODE_R", "ISL29125_MODE_G", "ISL29125_MODE_B",
         "ISL29125_MODE_RG", "ISL29125_MODE_GB"};
 
-    for (size_t i = 0; i < sizeof(modes); i++) {
+    for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
         printf("Setting mode %s\n", mode_names[i]);
         isl29125_set_mode(&dev, modes[i]);
         xtimer_usleep(SLEEP);