diff --git a/devices/geiger/gqgmc.go b/devices/geiger/gqgmc.go
index 95cedb2af2f5eefb1e8d82d0784e251e10e5c889..02a0191a35d6fea7aab31752e3ace114b2dbe8da 100644
--- a/devices/geiger/gqgmc.go
+++ b/devices/geiger/gqgmc.go
@@ -240,7 +240,7 @@ func (gc *GQGMCCounter) setTimeParts(t time.Time) {
 }
 
 func (gc *GQGMCCounter) setTimeAll(t time.Time) {
-	cmd := make([]byte, 13)
+	cmd := make([]byte, 20)
 	copy(cmd[:], "<SETDATETIME")
 	cmd[12] = uint8(t.Year())
 	cmd[13] = uint8(int(t.Month()))