diff --git a/dtc.c b/dtc.c
index 3962d3f..bc786c5 100644
--- a/dtc.c
+++ b/dtc.c
@@ -12,7 +12,7 @@
  * Command line options
  */
 int quiet;		/* Level of quietness */
-int reservenum;		/* Number of memory reservation slots */
+unsigned int reservenum;/* Number of memory reservation slots */
 int minsize;		/* Minimum blob size */
 int padsize;		/* Additional padding to blob */
 int alignsize;		/* Additional padding to blob accroding to the alignsize */
@@ -197,7 +197,7 @@ int main(int argc, char *argv[])
 			depname = optarg;
 			break;
 		case 'R':
-			reservenum = strtol(optarg, NULL, 0);
+			reservenum = strtoul(optarg, NULL, 0);
 			break;
 		case 'S':
 			minsize = strtol(optarg, NULL, 0);
diff --git a/dtc.h b/dtc.h
index 6296361..47664f2 100644
--- a/dtc.h
+++ b/dtc.h
@@ -35,7 +35,7 @@
  * Command line options
  */
 extern int quiet;		/* Level of quietness */
-extern int reservenum;		/* Number of memory reservation slots */
+extern unsigned int reservenum;	/* Number of memory reservation slots */
 extern int minsize;		/* Minimum blob size */
 extern int padsize;		/* Additional padding to blob */
 extern int alignsize;		/* Additional padding to blob accroding to the alignsize */
diff --git a/flattree.c b/flattree.c
index 4659afb..3d0204f 100644
--- a/flattree.c
+++ b/flattree.c
@@ -295,7 +295,7 @@ static struct data flatten_reserve_list(struct reserve_info *reservelist,
 {
 	struct reserve_info *re;
 	struct data d = empty_data;
-	int    j;
+	unsigned int j;
 
 	for (re = reservelist; re; re = re->next) {
 		d = data_append_re(d, re->address, re->size);