diff --git a/ngrep.c b/ngrep.c
index 59de008..c2a8aa9 100644
--- a/ngrep.c
+++ b/ngrep.c
@@ -104,8 +104,9 @@
  * Configuration Options
  */
 
-uint16_t snaplen = 65535, limitlen = 65535, promisc = 1, to = 100;
-uint16_t match_after = 0, keep_matching = 0, matches = 0, max_matches = 0;
+uint32_t snaplen = 65535, limitlen = 65535, promisc = 1, to = 100;
+uint32_t match_after = 0, keep_matching = 0, matches = 0, max_matches = 0;
+
 #if USE_TCPKILL
 uint16_t tcpkill_active = 0;
 #endif
@@ -232,9 +233,10 @@ int main(int argc, char **argv) {
             case 'P':
                 nonprint_char = *optarg;
                 break;
-            case 'S':
-                limitlen = atoi(optarg);
+            case 'S': {
+                limitlen = _atoui32(optarg);
                 break;
+            }
             case 'O':
                 dump_file = optarg;
                 break;
@@ -242,7 +244,9 @@ int main(int argc, char **argv) {
                 read_file = optarg;
                 break;
             case 'A':
-                match_after = atoi(optarg) + 1;
+                match_after = _atoui32(optarg);
+                if (match_after < UINT32_MAX)
+                    match_after++;
                 break;
 #if defined(_WIN32)
             case 'L':
@@ -263,10 +267,10 @@ int main(int argc, char **argv) {
                 ws_col_forced = atoi(optarg);
                 break;
             case 'n':
-                max_matches = atoi(optarg);
+                max_matches = _atoui32(optarg);
                 break;
             case 's': {
-                uint16_t value = atoi(optarg);
+                uint16_t value = _atoui32(optarg);
                 if (value > 0)
                     snaplen = value;
             } break;
diff --git a/ngrep.h b/ngrep.h
index 2ba85e5..9b9a50b 100644
--- a/ngrep.h
+++ b/ngrep.h
@@ -35,6 +35,9 @@
   ((uint16_t)((uint16_t)*((const uint8_t *)(p) + 0) << 8 | \
            (uint16_t)*((const uint8_t *)(p) + 1)))
 
+#define _atoui32(p) \
+  ((uint32_t)strtoul((p), (char **)NULL, 10))
+
 /*
  * Default patterns for BPF and regular expression filters.
  *