diff --git a/qemu-nbd.c b/qemu-nbd.c
index 598caa656b..efca0e44a9 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -546,9 +546,8 @@ int main(int argc, char **argv)
     };
     int ch;
     int opt_ind = 0;
-    char *end;
     int flags = BDRV_O_RDWR;
-    int partition = -1;
+    int partition = 0;
     int ret = 0;
     bool seen_cache = false;
     bool seen_discard = false;
@@ -660,9 +659,8 @@ int main(int argc, char **argv)
             port = optarg;
             break;
         case 'o':
-                dev_offset = strtoll (optarg, &end, 0);
-            if (*end) {
-                error_report("Invalid offset `%s'", optarg);
+            if (qemu_strtou64(optarg, NULL, 0, &dev_offset) < 0) {
+                error_report("Invalid offset '%s'", optarg);
                 exit(EXIT_FAILURE);
             }
             break;
@@ -684,13 +682,9 @@ int main(int argc, char **argv)
             flags &= ~BDRV_O_RDWR;
             break;
         case 'P':
-            partition = strtol(optarg, &end, 0);
-            if (*end) {
-                error_report("Invalid partition `%s'", optarg);
-                exit(EXIT_FAILURE);
-            }
-            if (partition < 1 || partition > 8) {
-                error_report("Invalid partition %d", partition);
+            if (qemu_strtoi(optarg, NULL, 0, &partition) < 0 ||
+                partition < 1 || partition > 8) {
+                error_report("Invalid partition '%s'", optarg);
                 exit(EXIT_FAILURE);
             }
             break;
@@ -711,15 +705,11 @@ int main(int argc, char **argv)
             device = optarg;
             break;
         case 'e':
-            shared = strtol(optarg, &end, 0);
-            if (*end) {
+            if (qemu_strtoi(optarg, NULL, 0, &shared) < 0 ||
+                shared < 1) {
                 error_report("Invalid shared device number '%s'", optarg);
                 exit(EXIT_FAILURE);
             }
-            if (shared < 1) {
-                error_report("Shared device number must be greater than 0");
-                exit(EXIT_FAILURE);
-            }
             break;
         case 'f':
             fmt = optarg;
@@ -1007,7 +997,7 @@ int main(int argc, char **argv)
     }
     fd_size -= dev_offset;
 
-    if (partition != -1) {
+    if (partition) {
         uint64_t limit;
 
         if (dev_offset) {