diff --git a/src/common/gamecode/economy.c b/src/common/gamecode/economy.c
index 95f4fe064..f08dccfcc 100644
--- a/src/common/gamecode/economy.c
+++ b/src/common/gamecode/economy.c
@@ -1624,6 +1624,8 @@ make_cmd(unit * u, struct order * ord)
 	const char *s;
   const struct locale * lang = u->faction->locale;
   
+  if (u->number==NULL) return;
+
   init_tokens(ord);
   skip_token();
   s = getstrtoken();
diff --git a/src/common/gamecode/laws.c b/src/common/gamecode/laws.c
index d5b2e3979..0db59f390 100644
--- a/src/common/gamecode/laws.c
+++ b/src/common/gamecode/laws.c
@@ -338,7 +338,7 @@ age_unit(region * r, unit * u)
     }
   } else {
     ++u->age;
-    if (u->race->age) {
+    if (u->number>0 && u->race->age) {
       u->race->age(u);
     }
   }
diff --git a/src/common/gamecode/randenc.c b/src/common/gamecode/randenc.c
index 728767164..0fa4fc9a8 100644
--- a/src/common/gamecode/randenc.c
+++ b/src/common/gamecode/randenc.c
@@ -309,6 +309,7 @@ static void
 get_allies(region * r, unit * u)
 {
 	unit *newunit = NULL;
+  assert(u->number);
 
 	switch (rterrain(r)) {
 
@@ -422,27 +423,24 @@ void
 encounters(void)
 {
 	region *r;
-	unit *u;
-	int n;
-	int c;
-	int i;
 
 	for (r = regions; r; r = r->next) {
 		if (!fval(r->terrain, SEA_REGION) && fval(r, RF_ENCOUNTER)) {
-			c = 0;
+			int c = 0;
+      unit * u;
 			for (u = r->units; u; u = u->next) {
 				c += u->number;
 			}
 
 			if (c > 0) {
-				n = rng_int() % c;
-				u = r->units;
+        int i = 0;
+				int n = rng_int() % c;
 
-				for (i = u->number; i < n; i += u->number) {
-					u = u->next;
+        for (u = r->units; u; u = u->next) {
+					if (i+u->number>c) break;
 				}
-
-				encounter(r, u);
+        assert(u && u->number);
+        encounter(r, u);
 			}
 		}
 	}
@@ -609,12 +607,13 @@ damage_unit(unit *u, const char *dam, boolean physical, boolean magic)
   int *hp = malloc(u->number * sizeof(int));
   int   h;
   int   i, dead = 0, hp_rem = 0, heiltrank;
+  double magres = magic_resistance(u);
 
+  assert(u->number);
   if (fval(u->race, RCF_ILLUSIONARY) || u->race == new_race[RC_SPELL]) {
     return 0;
   }
 
-  if (u->number==0) return 0;
   h = u->hp/u->number;
   /* HP verteilen */
   for (i=0; i<u->number; i++) hp[i] = h;
@@ -624,7 +623,7 @@ damage_unit(unit *u, const char *dam, boolean physical, boolean magic)
   /* Schaden */
   for (i=0; i<u->number; i++) {
     int damage = dice_rand(dam);
-    if (magic) damage = (int)(damage * (1.0 - magic_resistance(u)));
+    if (magic) damage = (int)(damage * (1.0 - magres));
     if (physical) damage -= nb_armor(u, i);
     hp[i] -= damage;
   }
@@ -766,19 +765,21 @@ volcano_outbreak(region *r)
 
   for (up=&r->units; *up;) {
     unit * u = *up;
-    int dead = damage_unit(u, "4d10", true, false);
-    if (dead) {
-      ADDMSG(&u->faction->msgs, msg_message("volcano_dead", 
-        "unit region dead", u, r, dead));
-    }
-    if (!fval(u->faction, FL_DH)) {
-      fset(u->faction, FL_DH);
-      if (rn) {
-        ADDMSG(&u->faction->msgs, msg_message("volcanooutbreak", 
-          "regionv regionn", r, rn));
-      } else {
-        ADDMSG(&u->faction->msgs, msg_message("volcanooutbreaknn", 
-          "region", r));
+    if (u->number) {
+      int dead = damage_unit(u, "4d10", true, false);
+      if (dead) {
+        ADDMSG(&u->faction->msgs, msg_message("volcano_dead", 
+          "unit region dead", u, r, dead));
+      }
+      if (!fval(u->faction, FL_DH)) {
+        fset(u->faction, FL_DH);
+        if (rn) {
+          ADDMSG(&u->faction->msgs, msg_message("volcanooutbreak", 
+            "regionv regionn", r, rn));
+        } else {
+          ADDMSG(&u->faction->msgs, msg_message("volcanooutbreaknn", 
+            "region", r));
+        }
       }
     }
     if (u==*up) up=&u->next;
@@ -805,10 +806,12 @@ volcano_outbreak(region *r)
     /* Personen bekommen 3W10 Punkte Schaden. */
     for (up=&rn->units; *up;) {
       unit * u = *up;
-      int dead = damage_unit(u, "3d10", true, false);
-      if (dead) {
-        ADDMSG(&u->faction->msgs, msg_message("volcano_dead", 
-          "unit region dead", u, r, dead));
+      if (u->number) {
+        int dead = damage_unit(u, "3d10", true, false);
+        if (dead) {
+          ADDMSG(&u->faction->msgs, msg_message("volcano_dead", 
+            "unit region dead", u, r, dead));
+        }
       }
       if (u==*up) up=&u->next;
     }
diff --git a/src/common/gamecode/study.c b/src/common/gamecode/study.c
index 7402041b3..fdebc8909 100644
--- a/src/common/gamecode/study.c
+++ b/src/common/gamecode/study.c
@@ -446,11 +446,7 @@ learn_cmd(unit * u, order * ord)
   int p;
   magic_t mtyp;
   int l;
-  int studycost;
-
-  /* lernen nach lehren */
-
-  int days;
+  int studycost, days;
   double multi = 1.0;
   attrib * a = NULL;
   teaching_info * teach = NULL;
@@ -458,6 +454,7 @@ learn_cmd(unit * u, order * ord)
   skill_t sk;
   int maxalchemy = 0;
 
+  if (u->number==0) return;
   if (fval(r->terrain, SEA_REGION)) {
     /* sonderbehandlung aller die auf Ozeanen lernen können */
     if (u->race!=new_race[RC_AQUARIAN] && !(u->race->flags & RCF_SWIM)) {
diff --git a/src/common/kernel/battle.c b/src/common/kernel/battle.c
index dce9f8a28..15ea60a70 100644
--- a/src/common/kernel/battle.c
+++ b/src/common/kernel/battle.c
@@ -911,6 +911,7 @@ terminate(troop dt, troop at, int type, const char *damage, boolean missile)
   boolean magic = false;
   int da = dice_rand(damage);
 
+  assert(du->number>0);
 #ifdef SHOW_KILLS
   ++at.fighter->hits;
 #endif
@@ -2914,6 +2915,7 @@ make_fighter(battle * b, unit * u, side * s1, boolean attack)
   static boolean init = false;
   unsigned int flags = 0;
 
+  assert(u->number);
   if (fval(u, UFL_PARTEITARNUNG)!=0) flags |= SIDE_STEALTH;
 #ifdef SIMPLE_COMBAT
   if (attack) flags |= SIDE_ATTACKER;
diff --git a/src/common/kernel/build.c b/src/common/kernel/build.c
index ef4d72251..c5f627218 100644
--- a/src/common/kernel/build.c
+++ b/src/common/kernel/build.c
@@ -452,6 +452,7 @@ build_road(region * r, unit * u, int size, direction_t d)
   int n, left;
   region * rn = rconnect(r,d);
 
+  assert(u->number);
   if (!eff_skill(u, SK_ROAD_BUILDING, r)) {
     cmistake(u, u->thisorder, 103, MSG_PRODUCE);
     return;
@@ -611,6 +612,7 @@ build(unit * u, const construction * ctype, int completed, int want)
   int made = 0;
   int basesk, effsk;
 
+  assert(u->number);
   if (want<=0) return 0;
   if (type==NULL) return 0;
   if (type->improvement==NULL && completed==type->maxsize)
@@ -796,6 +798,7 @@ build_building(unit * u, const building_type * btype, int want, order * ord)
   order * new_order = NULL;
   const struct locale * lang = u->faction->locale;
 
+  assert(u->number);
   if (eff_skill(u, SK_BUILDING, r) == 0) {
     cmistake(u, ord, 101, MSG_PRODUCE);
     return;
diff --git a/src/common/kernel/curse.c b/src/common/kernel/curse.c
index abdee24be..35475ce70 100644
--- a/src/common/kernel/curse.c
+++ b/src/common/kernel/curse.c
@@ -546,7 +546,7 @@ create_curse(unit *magician, attrib **ap, const curse_type *ct, double vigour,
 /* hier müssen alle c-typen, die auf Einheiten gezaubert werden können,
  * berücksichtigt werden */
 
-void
+static void
 do_transfer_curse(curse *c, unit * u, unit * u2, int n)
 {
   int flag = c->flag;
diff --git a/src/common/kernel/eressea.c b/src/common/kernel/eressea.c
index 41cd77f87..ca791182d 100644
--- a/src/common/kernel/eressea.c
+++ b/src/common/kernel/eressea.c
@@ -881,7 +881,7 @@ scale_number (unit * u, int n)
   int remain;
 
   if (n == u->number) return;
-  if (n && u->number) {
+  if (n && u->number>0) {
     int full;
     remain = ((u->hp%u->number) * (n % u->number)) % u->number;
 
@@ -894,17 +894,19 @@ scale_number (unit * u, int n)
     remain = 0;
     u->hp = 0;
   }
-  for (a = a_find(u->attribs, &at_effect);a && a->type==&at_effect;a=a->next) {
-    effect_data * data = (effect_data *)a->data.v;
-    int snew = data->value / u->number * n;
-    if (n) {
-      remain = data->value - snew / n * u->number;
-      snew += remain * n / u->number;
-      remain = (remain * n) % u->number;
-      if ((rng_int() % u->number) < remain)
-        ++snew; /* Nachkommastellen */
+  if (u->number>0) {
+    for (a = a_find(u->attribs, &at_effect);a && a->type==&at_effect;a=a->next) {
+      effect_data * data = (effect_data *)a->data.v;
+      int snew = data->value / u->number * n;
+      if (n) {
+        remain = data->value - snew / n * u->number;
+        snew += remain * n / u->number;
+        remain = (remain * n) % u->number;
+        if ((rng_int() % u->number) < remain)
+          ++snew; /* Nachkommastellen */
+      }
+      data->value = snew;
     }
-    data->value = snew;
   }
   if (u->number==0 || n==0) {
     for (sk = 0; sk < MAXSKILLS; sk++) {
diff --git a/src/common/kernel/magic.c b/src/common/kernel/magic.c
index b5ce877ed..81f0347f9 100644
--- a/src/common/kernel/magic.c
+++ b/src/common/kernel/magic.c
@@ -1085,6 +1085,7 @@ magic_resistance(unit *target)
 
   /* Bonus durch Rassenmagieresistenz */
   double probability = target->race->magres;
+  assert(target->number>0);
 
   /* Magier haben einen Resistenzbonus vom Magietalent * 5%*/
   probability += effskill(target, SK_MAGIC)*0.05;
diff --git a/src/common/kernel/movement.c b/src/common/kernel/movement.c
index 7304b5f49..523d75f3e 100644
--- a/src/common/kernel/movement.c
+++ b/src/common/kernel/movement.c
@@ -1249,6 +1249,7 @@ movement_speed(unit * u)
   static boolean init = false;
   double dk = u->race->speed;
 
+  assert(u->number);
   /* dragons have a fixed speed, and no other effects work on them: */
   switch (old_race(u->race)) {
     case RC_DRAGON:
@@ -2051,6 +2052,7 @@ move(unit * u, boolean move_on_land)
 {
   region_list * route = NULL;
 
+  assert(u->number);
   if (u->ship && fval(u, UFL_OWNER)) {
     sail(u, u->thisorder, move_on_land, &route);
   } else {
diff --git a/src/common/kernel/reports.c b/src/common/kernel/reports.c
index 35211a605..5e29845d6 100644
--- a/src/common/kernel/reports.c
+++ b/src/common/kernel/reports.c
@@ -132,6 +132,7 @@ hp_status(const unit * u)
 void
 report_item(const unit * owner, const item * i, const faction * viewer, const char ** name, const char ** basename, int * number, boolean singular)
 {
+  assert(owner->number);
 	if (owner->faction == viewer) {
 		if (name) *name = locale_string(viewer->locale, resourcename(i->type->rtype, ((i->number!=1 && !singular)?GR_PLURAL:0)));
 		if (basename) *basename = resourcename(i->type->rtype, 0);
diff --git a/src/common/kernel/save.c b/src/common/kernel/save.c
index a2d2e5eb5..3fb0c0eaa 100644
--- a/src/common/kernel/save.c
+++ b/src/common/kernel/save.c
@@ -1077,16 +1077,18 @@ readunit(FILE * F)
 	assert(u->race);
 	if (global.data_version<NEWSKILL_VERSION) {
 		/* convert old data */
-		while ((sk = (skill_t) ri(F)) != NOSKILL) {
-			int days = ri(F) / u->number;
-			int lvl = level(days);
-			int weeks = lvl + 1 - (days - level_days(lvl))/30;
-			assert(weeks>0 && weeks<=lvl+1);
-			if (lvl) {
-				skill * sv = add_skill(u, sk);
-				sv->level = sv->old = (unsigned char)lvl;
-				sv->weeks = (unsigned char)weeks;
-			}
+    if (u->number) {
+      while ((sk = (skill_t) ri(F)) != NOSKILL) {
+			  int days = ri(F) / u->number;
+			  int lvl = level(days);
+			  int weeks = lvl + 1 - (days - level_days(lvl))/30;
+			  assert(weeks>0 && weeks<=lvl+1);
+			  if (lvl) {
+				  skill * sv = add_skill(u, sk);
+				  sv->level = sv->old = (unsigned char)lvl;
+				  sv->weeks = (unsigned char)weeks;
+			  }
+      }
 		}
 	} else {
 		while ((sk = (skill_t) ri(F)) != NOSKILL) {
diff --git a/src/common/kernel/unit.c b/src/common/kernel/unit.c
index 9f8f25546..b2b15f9ec 100644
--- a/src/common/kernel/unit.c
+++ b/src/common/kernel/unit.c
@@ -782,8 +782,8 @@ transfermen(unit * u, unit * u2, int n)
 	int hp = u->hp;
 	region * r = u->region;
 
-	if (!n) return;
-
+	if (n==0) return;
+  assert(n > 0);
 	/* "hat attackiert"-status wird übergeben */
 
 	if (u2) {
diff --git a/src/common/races/dragons.c b/src/common/races/dragons.c
index ad3a9a39d..2185c24fb 100644
--- a/src/common/races/dragons.c
+++ b/src/common/races/dragons.c
@@ -31,7 +31,7 @@
 void
 age_firedragon(unit *u)
 {
-	if (rng_int()%100 < age_chance(u->age, DRAGONAGE, 1)) {
+	if (u->number>0 && rng_int()%100 < age_chance(u->age, DRAGONAGE, 1)) {
 		double q = (double) u->hp / (double) (unit_max_hp(u) * u->number);
 		u->race = new_race[RC_DRAGON];
 		u->irace = new_race[RC_DRAGON];
@@ -43,7 +43,7 @@ age_firedragon(unit *u)
 void
 age_dragon(unit *u)
 {
-	if (rng_int()%100 < age_chance(u->age, WYRMAGE, 1)) {
+	if (u->number>0 && rng_int()%100 < age_chance(u->age, WYRMAGE, 1)) {
 		double q = (double) u->hp / (double) (unit_max_hp(u) * u->number);
 		u->race = new_race[RC_WYRM];
 		u->irace = new_race[RC_WYRM];
diff --git a/src/common/spells/spells.c b/src/common/spells/spells.c
index 2ca49b5dc..10a2e9d97 100644
--- a/src/common/spells/spells.c
+++ b/src/common/spells/spells.c
@@ -4708,7 +4708,7 @@ sp_headache(castorder *co)
   countspells(mage, 1);
 
   /* wenn kein Ziel gefunden, Zauber abbrechen */
-  if(pa->param[0]->flag == TARGET_NOTFOUND) return 0;
+  if (target->number==0 || pa->param[0]->flag == TARGET_NOTFOUND) return 0;
 
   target = pa->param[0]->data.u; /* Zieleinheit */