diff --git a/src/components/BalanceAssertionEditor.vue b/src/components/BalanceAssertionEditor.vue
index 1ad2801..75b657d 100644
--- a/src/components/BalanceAssertionEditor.vue
+++ b/src/components/BalanceAssertionEditor.vue
@@ -47,14 +47,26 @@
 		<button class="btn-secondary text-red-600 ring-red-500" @click="deleteAssertion" v-if="assertion.id !== null">Delete</button>
 		<button class="btn-primary" @click="saveAssertion">Save</button>
 	</div>
+	
+	<div class="rounded-md bg-red-50 mt-4 p-4 col-span-2" v-if="error !== null">
+		<div class="flex">
+			<div class="flex-shrink-0">
+				<XCircleIcon class="h-5 w-5 text-red-400" />
+			</div>
+			<div class="ml-3 flex-1">
+				<p class="text-sm text-red-700">{{ error }}</p>
+			</div>
+		</div>
+	</div>
 </template>
 
 <script setup lang="ts">
 	import dayjs from 'dayjs';
-	
+	import { XCircleIcon } from '@heroicons/vue/24/solid';
 	import { getCurrentWindow } from '@tauri-apps/api/window';
+	import { ref } from 'vue';
 	
-	import { DT_FORMAT, db, deserialiseAmount } from '../db.ts';
+	import { DeserialiseAmountError, DT_FORMAT, db, deserialiseAmount } from '../db.ts';
 	import ComboBoxAccounts from './ComboBoxAccounts.vue';
 	
 	export interface EditingAssertion {
@@ -68,9 +80,23 @@
 	
 	const { assertion } = defineProps<{ assertion: EditingAssertion }>();
 	
+	const error = ref(null as string | null);
+	
 	async function saveAssertion() {
 		// Save changes to the assertion
-		const amount_abs = deserialiseAmount('' + assertion.amount_abs);
+		error.value = null;
+		
+		let amount_abs;
+		try {
+			amount_abs = deserialiseAmount('' + assertion.amount_abs);
+		} catch (err) {
+			if (err instanceof DeserialiseAmountError) {
+				error.value = err.message;
+				return;
+			} else {
+				throw err;
+			}
+		}
 		const quantity = assertion.sign === 'dr' ? amount_abs.quantity : -amount_abs.quantity;
 		
 		const session = await db.load();
@@ -90,6 +116,8 @@
 			);
 		}
 		
+		// TODO: Send event
+		
 		await getCurrentWindow().close();
 	}
 	
@@ -107,6 +135,8 @@
 			[assertion.id]
 		);
 		
+		// TODO: Send event
+		
 		await getCurrentWindow().close();
 	}
 </script>
diff --git a/src/components/TransactionEditor.vue b/src/components/TransactionEditor.vue
index 732a284..1e77895 100644
--- a/src/components/TransactionEditor.vue
+++ b/src/components/TransactionEditor.vue
@@ -109,7 +109,7 @@
 	
 	import { ref } from 'vue';
 	
-	import { DT_FORMAT, Posting, Transaction, db, deserialiseAmount } from '../db.ts';
+	import { DT_FORMAT, DeserialiseAmountError, Posting, Transaction, db, deserialiseAmount } from '../db.ts';
 	import ComboBoxAccounts from './ComboBoxAccounts.vue';
 	
 	interface EditingPosting {
@@ -155,7 +155,17 @@
 		);
 		
 		for (const posting of transaction.postings) {
-			const amount_abs = deserialiseAmount(posting.amount_abs);
+			let amount_abs;
+			try {
+				amount_abs = deserialiseAmount(posting.amount_abs);
+			} catch (err) {
+				if (err instanceof DeserialiseAmountError) {
+					error.value = err.message;
+					return;
+				} else {
+					throw err;
+				}
+			}
 			
 			newTransaction.postings.push({
 				id: posting.id,
diff --git a/src/db.ts b/src/db.ts
index 4f178bc..cff148c 100644
--- a/src/db.ts
+++ b/src/db.ts
@@ -176,7 +176,8 @@ export function deserialiseAmount(amount: string): { quantity: number, commodity
 		// Default commodity
 		const quantity = Math.round(parseFloat(amount) * factor)
 		
-		if (!Number.isSafeInteger(quantity)) { throw new Error('Quantity not representable by safe integer'); }
+		if (Number.isNaN(quantity)) { throw new DeserialiseAmountError('Invalid quantity: ' + amount); }
+		if (!Number.isSafeInteger(quantity)) { throw new DeserialiseAmountError('Quantity not representable by safe integer: ' + amount); }
 		
 		return {
 			'quantity': quantity,
@@ -189,7 +190,8 @@ export function deserialiseAmount(amount: string): { quantity: number, commodity
 	const quantityStr = amount.substring(0, amount.indexOf(' '));
 	const quantity = Math.round(parseFloat(quantityStr) * factor)
 	
-	if (!Number.isSafeInteger(quantity)) { throw new Error('Quantity not representable by safe integer'); }
+	if (Number.isNaN(quantity)) { throw new DeserialiseAmountError('Invalid quantity: ' + amount); }
+	if (!Number.isSafeInteger(quantity)) { throw new DeserialiseAmountError('Quantity not representable by safe integer: ' + amount); }
 	
 	const commodity = amount.substring(amount.indexOf(' ') + 1);
 	
@@ -199,6 +201,8 @@ export function deserialiseAmount(amount: string): { quantity: number, commodity
 	};
 }
 
+export class DeserialiseAmountError extends Error {}
+
 // Type definitions
 
 export class Transaction {
diff --git a/src/plugins/austax/CGTAdjustmentEditor.vue b/src/plugins/austax/CGTAdjustmentEditor.vue
index 8c71f8f..5174caf 100644
--- a/src/plugins/austax/CGTAdjustmentEditor.vue
+++ b/src/plugins/austax/CGTAdjustmentEditor.vue
@@ -60,14 +60,27 @@
 		<button class="btn-secondary text-red-600 ring-red-500" @click="deleteAdjustment" v-if="adjustment.id !== null">Delete</button>
 		<button class="btn-primary" @click="saveAdjustment">Save</button>
 	</div>
+	
+	<div class="rounded-md bg-red-50 mt-4 p-4 col-span-2" v-if="error !== null">
+		<div class="flex">
+			<div class="flex-shrink-0">
+				<XCircleIcon class="h-5 w-5 text-red-400" />
+			</div>
+			<div class="ml-3 flex-1">
+				<p class="text-sm text-red-700">{{ error }}</p>
+			</div>
+		</div>
+	</div>
 </template>
 
 <script setup lang="ts">
 	import dayjs from 'dayjs';
+	import { XCircleIcon } from '@heroicons/vue/24/solid';
 	import { getCurrentWindow } from '@tauri-apps/api/window';
+	import { ref } from 'vue';
 	
 	import ComboBoxAccounts from '../../components/ComboBoxAccounts.vue';
-	import { DT_FORMAT, db, deserialiseAmount } from '../../db.ts';
+	import { DT_FORMAT, DeserialiseAmountError, db, deserialiseAmount } from '../../db.ts';
 	
 	export interface EditingCGTAdjustment {
 		id: number | null,
@@ -82,10 +95,36 @@
 	
 	const { adjustment } = defineProps<{ adjustment: EditingCGTAdjustment }>();
 	
+	const error = ref(null as string | null);
+	
 	async function saveAdjustment() {
 		// Save changes to the CGT adjustment
-		const asset = deserialiseAmount('' + adjustment.asset);
-		const cost_adjustment_abs = deserialiseAmount('' + adjustment.cost_adjustment_abs);
+		error.value = null;
+		
+		let asset;
+		try {
+			asset = deserialiseAmount(adjustment.asset);
+		} catch (err) {
+			if (err instanceof DeserialiseAmountError) {
+				error.value = err.message;
+				return;
+			} else {
+				throw err;
+			}
+		}
+		
+		let cost_adjustment_abs;
+		try {
+			cost_adjustment_abs = deserialiseAmount(adjustment.cost_adjustment_abs);
+		} catch (err) {
+			if (err instanceof DeserialiseAmountError) {
+				error.value = err.message;
+				return;
+			} else {
+				throw err;
+			}
+		}
+		
 		const cost_adjustment = adjustment.sign === 'dr' ? cost_adjustment_abs.quantity : -cost_adjustment_abs.quantity;
 		
 		const session = await db.load();
diff --git a/src/plugins/austax/MultiNewCGTAdjustmentView.vue b/src/plugins/austax/MultiNewCGTAdjustmentView.vue
index 3ff9618..f310a97 100644
--- a/src/plugins/austax/MultiNewCGTAdjustmentView.vue
+++ b/src/plugins/austax/MultiNewCGTAdjustmentView.vue
@@ -70,18 +70,31 @@
 	<div class="flex justify-end mt-4 space-x-2">
 		<button class="btn-primary" @click="saveAdjustment">Save</button>
 	</div>
+	
+	<div class="rounded-md bg-red-50 mt-4 p-4 col-span-2" v-if="error !== null">
+		<div class="flex">
+			<div class="flex-shrink-0">
+				<XCircleIcon class="h-5 w-5 text-red-400" />
+			</div>
+			<div class="ml-3 flex-1">
+				<p class="text-sm text-red-700">{{ error }}</p>
+			</div>
+		</div>
+	</div>
 </template>
 
 <script setup lang="ts">
 	import dayjs from 'dayjs';
+	import { XCircleIcon } from '@heroicons/vue/24/solid';
 	import { InformationCircleIcon } from '@heroicons/vue/20/solid';
 	import { getCurrentWindow } from '@tauri-apps/api/window';
 	import { ref } from 'vue';
 	
 	import { CGTAsset } from './cgt.ts';
 	import ComboBoxAccounts from '../../components/ComboBoxAccounts.vue';
-	import { DT_FORMAT, JoinedTransactionPosting, db, deserialiseAmount } from '../../db.ts';
+	import { DT_FORMAT, DeserialiseAmountError, JoinedTransactionPosting, db, deserialiseAmount } from '../../db.ts';
 	import { ppWithCommodity } from '../../display.ts';
+	import { CriticalError } from '../../error.ts';
 	
 	const account = ref('');
 	const commodity = ref('');
@@ -90,10 +103,25 @@
 	const cost_adjustment_abs = ref(null! as number);
 	const sign = ref('dr');
 	
+	const error = ref(null as string | null);
+	
 	async function saveAdjustment() {
 		// TODO: Preview mode?
 		
-		const totalAdjustmentAbs = deserialiseAmount('' + cost_adjustment_abs.value);
+		error.value = null;
+		
+		let totalAdjustmentAbs;
+		try {
+			totalAdjustmentAbs = deserialiseAmount('' + cost_adjustment_abs.value);
+		} catch (err) {
+			if (err instanceof DeserialiseAmountError) {
+				error.value = err.message;
+				return;
+			} else {
+				throw err;
+			}
+		}
+		
 		const totalAdjustment = sign.value === 'dr' ? totalAdjustmentAbs.quantity : -totalAdjustmentAbs.quantity;
 		
 		// Get all postings to the CGT asset account
@@ -149,7 +177,8 @@
 		}
 		
 		if (assets.length === 0) {
-			throw new Error('No matching CGT assets');
+			error.value = 'No matching CGT assets';
+			return;
 		}
 		
 		// Distribute total adjustment across matching assets
@@ -192,7 +221,7 @@
 		// Sanity check
 		const totalRoundedAdjustment = cgtAdjustments.reduce((acc, adj) => acc + adj, 0);
 		if (totalRoundedAdjustment !== totalAdjustment) {
-			throw new Error('Rounding unexpectedly changed total CGT adjustment amount');
+			throw new CriticalError('Rounding unexpectedly changed total CGT adjustment amount');
 		}
 		
 		// Add adjustments to database atomically