diff --git a/src/mission.c b/src/mission.c
index 32ac0b7..889d706 100644
--- a/src/mission.c
+++ b/src/mission.c
@@ -160,6 +160,7 @@ static int mission_alreadyRunning(MissionData* misn) {
 /* Is the lua condition for misn met? */
 static lua_State* mission_cond_L = NULL;
 static int mission_meetCond(MissionData* misn) {
+  int b;
   int ret;
   char buf[256];
 
@@ -201,8 +202,11 @@ static int mission_meetCond(MissionData* misn) {
       break;
   }
 
+  /* Check the result. */
   if(lua_isboolean(mission_cond_L, -1)) {
-    if(lua_toboolean(mission_cond_L, -1))
+    b = lua_toboolean(mission_cond_L, -1);
+    lua_pop(mission_cond_L, 1);
+    if(b)
       return 1;
     else
       return 0;