diff --git a/src/mode/SpaceInvaders/SpaceInvaders.h b/src/mode/SpaceInvaders/SpaceInvaders.h
index 479f316..acadfcf 100644
--- a/src/mode/SpaceInvaders/SpaceInvaders.h
+++ b/src/mode/SpaceInvaders/SpaceInvaders.h
@@ -89,7 +89,7 @@ public:
     void stepRockets(microseconds_t dt) {
       rocketRuntime += dt;
       if (rocketRuntime > 200000) {
-        rocketRuntime -= 200000;
+        rocketRuntime = rocketRuntime % 200000;
         for (Rocket *rocket = rocketsBegin; rocket < rocketsEnd; rocket++) {
           if (rocket->alive) {
             if (rocket->y == 0) {
@@ -117,7 +117,7 @@ public:
       }
 
       if (swarmRuntime >= 1000000) {
-        swarmRuntime -= 1000000;
+        swarmRuntime = swarmRuntime % 1000000;
         if (swarmLeft) {
           swarmX--;
           if (swarmX == 0) {
@@ -138,7 +138,7 @@ public:
     void stepHero(microseconds_t dt) {
       heroRuntime += dt;
       if (heroRuntime >= 50000) {
-        heroRuntime -= 50000;
+        heroRuntime = heroRuntime % 50000;
         if (heroLeft) {
           heroX--;
           if (heroX <= 1 || randomBool(20)) {