diff --git a/deco.c b/deco.c
index 16089e32b..6f8f0f6d4 100644
--- a/deco.c
+++ b/deco.c
@@ -362,6 +362,9 @@ void boyles_law(double next_stop_pressure)
 {
 	int ci;
 
+	if (!in_planner() || prefs.deco_mode != VPMB)
+		return;
+
 	// This should be a tautology but prevents a numerical instability.
 	if (IS_FP_SAME(next_stop_pressure, first_stop_pressure))
 		return;