diff --git a/src/udev/scsi_id/scsi_serial.c b/src/udev/scsi_id/scsi_serial.c
index 0abc8ca212..e1940e7d38 100644
--- a/src/udev/scsi_id/scsi_serial.c
+++ b/src/udev/scsi_id/scsi_serial.c
@@ -396,27 +396,21 @@ static int do_scsi_page0_inquiry(struct scsi_id_device *dev_scsi, int fd,
         return 0;
 }
 
-/*
- * The caller checks that serial is long enough to include the vendor +
- * model.
- */
-static int prepend_vendor_model(struct scsi_id_device *dev_scsi, char *serial) {
-        int ind;
+static int append_vendor_model(
+                const struct scsi_id_device *dev_scsi,
+                char buf[static VENDOR_LENGTH + MODEL_LENGTH]) {
 
-        strncpy(serial, dev_scsi->vendor, VENDOR_LENGTH);
-        strncat(serial, dev_scsi->model, MODEL_LENGTH);
-        ind = strlen(serial);
-
-        /*
-         * This is not a complete check, since we are using strncat/cpy
-         * above, ind will never be too large.
-         */
-        if (ind != (VENDOR_LENGTH + MODEL_LENGTH))
+        if (strnlen(dev_scsi->vendor, VENDOR_LENGTH) != VENDOR_LENGTH)
                 return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
-                                       "%s: expected length %d, got length %d",
-                                       dev_scsi->kernel,
-                                       (VENDOR_LENGTH + MODEL_LENGTH), ind);
-        return ind;
+                                       "%s: bad vendor string \"%s\"",
+                                       dev_scsi->kernel, dev_scsi->vendor);
+        if (strnlen(dev_scsi->model, MODEL_LENGTH) != MODEL_LENGTH)
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "%s: bad model string \"%s\"",
+                                       dev_scsi->kernel, dev_scsi->model);
+        memcpy(buf, dev_scsi->vendor, VENDOR_LENGTH);
+        memcpy(buf + VENDOR_LENGTH, dev_scsi->model, MODEL_LENGTH);
+        return VENDOR_LENGTH + MODEL_LENGTH;
 }
 
 /*
@@ -497,7 +491,7 @@ static int check_fill_0x83_id(struct scsi_id_device *dev_scsi,
          * included in the identifier.
          */
         if (id_search->id_type == SCSI_ID_VENDOR_SPECIFIC)
-                if (prepend_vendor_model(dev_scsi, serial + 1) < 0)
+                if (append_vendor_model(dev_scsi, serial + 1) < 0)
                         return 1;
 
         i = 4; /* offset to the start of the identifier */
@@ -731,7 +725,7 @@ static int do_scsi_page80_inquiry(struct scsi_id_device *dev_scsi, int fd,
         len = buf[3];
         if (serial) {
                 serial[0] = 'S';
-                ser_ind = prepend_vendor_model(dev_scsi, serial + 1);
+                ser_ind = append_vendor_model(dev_scsi, serial + 1);
                 if (ser_ind < 0)
                         return 1;
                 ser_ind++; /* for the leading 'S' */