diff --git a/syslinux/trunk/syslinux-install_update b/syslinux/trunk/syslinux-install_update
index ef2c6d7..a7ffdfd 100644
--- a/syslinux/trunk/syslinux-install_update
+++ b/syslinux/trunk/syslinux-install_update
@@ -199,7 +199,14 @@ get_boot_devices() {
             bootdevs[$slave]="$ptb"
         done
     else
-        local disk="${bootpart%%[[:digit:]]*}"
+        case "$bootpart" in
+            *[[:digit:]]p[[:digit:]]*)
+                local disk="${bootpart%%p$partnum}" # get everything before p1
+                ;;
+            *)
+                local disk="${bootpart%%[[:digit:]]*}"
+                ;;
+        esac
         device_is_gpt "$disk" && local ptb="GPT" || local ptb="MBR"
         bootdevs[$bootpart]="$ptb"
     fi