diff --git a/src/lib/commands/prod.c b/src/lib/commands/prod.c
index 16494b39..4f894cf3 100644
--- a/src/lib/commands/prod.c
+++ b/src/lib/commands/prod.c
@@ -87,7 +87,7 @@ prod(void)
     int wforce;
     i_type it;
     i_type vtype;
-    s_char *resource;
+    u_char *resource;
     s_char maxc[MAXPRCON][10];
     s_char use[MAXPRCON][10];
     int lcms, hcms;
@@ -204,7 +204,7 @@ prod(void)
 	    goto is_enlist;
 	if (pp->p_nrndx != 0) {
 	    unit_work++;
-	    resource = ((s_char *)&sect) + pp->p_nrndx;
+	    resource = (u_char *)&sect + pp->p_nrndx;
 	    p_e = (*resource * p_e) / 100.0;
 	}
 	/*
diff --git a/src/lib/update/produce.c b/src/lib/update/produce.c
index ee35f74a..6a69f2e2 100644
--- a/src/lib/update/produce.c
+++ b/src/lib/update/produce.c
@@ -57,7 +57,7 @@ produce(struct natstr *np, struct sctstr *sp, short *vec, int work,
     struct pchrstr *product;
     double p_e;
     double prodeff;
-    s_char *resource;
+    u_char *resource;
     double output;
     int actual;
     int unit_work;
@@ -82,7 +82,7 @@ produce(struct natstr *np, struct sctstr *sp, short *vec, int work,
     p_e = neweff / 100.0;
     if (product->p_nrndx != 0) {
 	unit_work++;
-	resource = ((s_char *)sp) + product->p_nrndx;
+	resource = (u_char *)sp + product->p_nrndx;
 	p_e = (*resource * p_e) / 100.0;
     }
     /*
diff --git a/src/lib/update/ship.c b/src/lib/update/ship.c
index 68adce71..861304a1 100644
--- a/src/lib/update/ship.c
+++ b/src/lib/update/ship.c
@@ -121,6 +121,7 @@ upd_ship(struct shpstr *sp, int etus,
     int max_food;
     struct pchrstr *product;
     s_char *resource;
+    int dep;
     int n;
     int mult;
     int needed;
@@ -180,9 +181,11 @@ upd_ship(struct shpstr *sp, int etus,
 		    oil_gained = max_oil - sp->shp_item[I_OIL];
 		sp->shp_item[I_OIL] += oil_gained;
 		if (product->p_nrdep != 0 && oil_gained > 0) {
-		    resource = ((s_char *)sectp) + product->p_nrndx;
-		    *resource -= roundavg(oil_gained *
-					  product->p_nrdep / 100.0);
+		    resource = (u_char *)sectp + product->p_nrndx;
+		    dep = roundavg(oil_gained * product->p_nrdep / 100.0);
+		    if (CANT_HAPPEN(dep > *resource))
+			dep = *resource;
+		    *resource -= dep;
 		}
 	    }
 	    if ((mp->m_flags & M_FOOD) && sectp->sct_type == SCT_WATER) {