diff --git a/src/speedo.c b/src/speedo.c
index 0b004b0..109db21 100644
--- a/src/speedo.c
+++ b/src/speedo.c
@@ -85,7 +85,7 @@ static int draw_fg(hexagram_gauge *gauge, cairo_t *cr) {
         goto error_dial_draw_fg;
     }
 
-    if (snprintf(buf, 8, "%d", (int)speedo->dial.value) < 0) {
+    if (snprintf(buf, sizeof(buf), "%d", (int)speedo->dial.value) < 0) {
         goto error_snprintf;
     }