diff --git a/zenno/src/lib/race.ts b/zenno/src/lib/race.ts
index 48dac19..969b3cb 100644
--- a/zenno/src/lib/race.ts
+++ b/zenno/src/lib/race.ts
@@ -283,6 +283,12 @@ export function speedGain(speedBonus: number, accel: number, decel: number, dur:
 	// and does not include the acceleration back to baseline after it ends.
 	const accelTime = speedBonus / accel;
 	const decelTime = -speedBonus / decel;
+	if (accelTime >= dur) {
+		// Acceleration is so low that the horse won't reach the boosted target
+		// speed before the effect ends. E.g., G surface aptitude.
+		const peakSpeed = accel * dur;
+		return 0.5 * (peakSpeed * dur - peakSpeed / decel);
+	}
 	// speedBonus*(dur-accelTime) + speedBonus*accelTime/2 + speedBonus*decelTime/2
 	return speedBonus * (dur + 0.5 * (decelTime - accelTime));
 }