diff --git a/src/playsim/p_mobj.cpp b/src/playsim/p_mobj.cpp
index 00d20722b..43d98ba25 100644
--- a/src/playsim/p_mobj.cpp
+++ b/src/playsim/p_mobj.cpp
@@ -149,6 +149,10 @@ FRandom pr_spawnmissile("SpawnMissile");
 
 CUSTOM_CVAR (Float, sv_gravity, 800.f, CVAR_SERVERINFO|CVAR_NOSAVE|CVAR_NOINITCALL)
 {
+	// test NAN and INF
+	if (((double)self != (double)self) || isinf((double)self))
+		sv_gravity = 800.f;
+
 	for (auto Level : AllLevels())
 	{
 		Level->gravity = self;