diff --git a/src/thingdef/thingdef_codeptr.cpp b/src/thingdef/thingdef_codeptr.cpp
index 4da9cea5f..0e5d44814 100644
--- a/src/thingdef/thingdef_codeptr.cpp
+++ b/src/thingdef/thingdef_codeptr.cpp
@@ -1337,7 +1337,8 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_FireCustomMissile)
 	AWeapon * weapon=player->ReadyWeapon;
 	AActor *linetarget;
 
-	if (UseAmmo && weapon)
+		// Only use ammo if called from a weapon
+	if (UseAmmo && ACTION_CALL_FROM_WEAPON() && weapon)
 	{
 		if (!weapon->DepleteAmmo(weapon->bAltFire, true)) return;	// out of ammo
 	}
@@ -5892,4 +5893,4 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_SetRipMax)
 	ACTION_PARAM_START(1);
 	ACTION_PARAM_INT(max, 1);
 	self->RipLevelMax = max;
-}
\ No newline at end of file
+}