Index: usr.sbin/bsdinstall/scripts/zfsboot
===================================================================
--- usr.sbin/bsdinstall/scripts/zfsboot
+++ usr.sbin/bsdinstall/scripts/zfsboot
@@ -287,10 +287,12 @@
 msg_stripe_help="[1+ Disks] Striping provides maximum storage but no redundancy"
 msg_swap_encrypt="Encrypt Swap?"
 msg_swap_encrypt_help="Encrypt swap partitions with temporary keys, discarded on reboot"
+msg_swap_invalid="The selected swap size (%s) is invalid. Enter a number optionally followed by units. Example: 2G"
 msg_swap_mirror="Mirror Swap?"
 msg_swap_mirror_help="Mirror swap partitions for redundancy, breaks crash dumps"
 msg_swap_size="Swap Size"
 msg_swap_size_help="Customize how much swap space is allocated to each selected disk"
+msg_swap_toosmall="The selected swap size (%s) is to small. Please enter a value greater than 100MB or enter 0 for no swap"
 msg_these_disks_are_too_small="These disks are too small given the amount of requested\nswap (%s) and/or geli(8) (%s) partitions, which would\ntake 50%% or more of each of the following selected disk\ndevices (not recommended):\n\n  %s\n\nRecommend changing partition size(s) and/or selecting a\ndifferent set of devices."
 msg_uefi_not_supported="The FreeBSD UEFI loader does not currently support booting root-on-ZFS. Your system will need to boot in legacy (CSM) mode.\nDo you want to continue?"
 msg_unable_to_get_disk_capacity="Unable to get disk capacity of \`%s'"
@@ -1554,10 +1556,26 @@
 		;;
 	?" $msg_swap_size")
 		# Prompt the user to input/change the swap size for each disk
-		f_dialog_input input \
-			"$msg_please_enter_amount_of_swap_space" \
-			"$ZFSBOOT_SWAP_SIZE" &&
-			ZFSBOOT_SWAP_SIZE="${input:-0}"
+		while :; do
+		    f_dialog_input input \
+			    "$msg_please_enter_amount_of_swap_space" \
+			    "$ZFSBOOT_SWAP_SIZE" &&
+			    ZFSBOOT_SWAP_SIZE="${input:-0}"
+		    if f_expand_number "$ZFSBOOT_SWAP_SIZE" swapsize
+		    then
+			if [ $swapsize -ne 0 -a $swapsize -lt 104857600 ]; then
+			    f_show_err "$msg_swap_toosmall" \
+				       "$ZFSBOOT_SWAP_SIZE"
+			    continue;
+			else
+			    break;
+			fi
+		    else
+			f_show_err "$msg_swap_invalid" \
+				   "$ZFSBOOT_SWAP_SIZE"
+			continue;
+		    fi
+		done
 		;;
 	?" $msg_swap_mirror")
 		# Toggle the variable referenced both by the menu and later