diff --git a/src/lib/currency.test.ts b/src/lib/currency.test.ts
new file mode 100644
index 0000000..3071fc7
--- /dev/null
+++ b/src/lib/currency.test.ts
@@ -0,0 +1,65 @@
+import { describe, expect, it } from "vitest";
+import {
+  CURRENCIES,
+  DEFAULT_CURRENCY,
+  formatCurrency,
+  formatCurrencyShort,
+} from "./currency";
+
+describe("formatCurrency", () => {
+  it("formats whole amounts with no minor units", () => {
+    // Use a non-breaking-space-tolerant check: Intl may insert NBSP.
+    const out = formatCurrency(1234, "USD");
+    expect(out).toContain("1,234");
+    expect(out).not.toContain(".00");
+  });
+
+  it("defaults to USD when no currency is given", () => {
+    expect(formatCurrency(10)).toBe(formatCurrency(10, DEFAULT_CURRENCY));
+  });
+
+  it("treats an empty-string currency as the default", () => {
+    expect(formatCurrency(10, "")).toBe(formatCurrency(10, DEFAULT_CURRENCY));
+  });
+
+  it("coerces non-finite values to 0", () => {
+    expect(formatCurrency(Number.NaN, "USD")).toContain("0");
+  });
+
+  it("renders a well-formed but unknown ISO code without throwing", () => {
+    // Intl is lenient here — it uses the code as the symbol.
+    const out = formatCurrency(1234, "ZZZ");
+    expect(out).toContain("ZZZ");
+    expect(out).toContain("1,234");
+  });
+
+  it("never throws on a structurally invalid code (no DB CHECK on deals.currency)", () => {
+    for (const bad of ["United States", "US", "USDD", "12", "u$d"]) {
+      expect(() => formatCurrency(1234, bad)).not.toThrow();
+      expect(formatCurrency(1234, bad)).toContain("1,234");
+    }
+  });
+
+  it("formats every offered currency without throwing", () => {
+    for (const c of CURRENCIES) {
+      expect(() => formatCurrency(1000, c.code)).not.toThrow();
+    }
+  });
+});
+
+describe("formatCurrencyShort", () => {
+  it("abbreviates millions and thousands with the currency symbol", () => {
+    expect(formatCurrencyShort(2_500_000, "USD")).toBe("$2.5M");
+    expect(formatCurrencyShort(3_400, "USD")).toBe("$3.4k");
+    expect(formatCurrencyShort(900, "USD")).toBe("$900");
+  });
+
+  it("uses the matching symbol for non-USD currencies", () => {
+    expect(formatCurrencyShort(1_000, "EUR")).toBe("€1.0k");
+    expect(formatCurrencyShort(1_000, "INR")).toBe("₹1.0k");
+  });
+
+  it("falls back to the code prefix for unknown currencies (no throw)", () => {
+    expect(formatCurrencyShort(1_000, "ZZZ")).toBe("ZZZ 1.0k");
+  });
+});
diff --git a/src/lib/currency.ts b/src/lib/currency.ts
index 46df731..c85f3eb 100644
--- a/src/lib/currency.ts
+++ b/src/lib/currency.ts
@@ -49,17 +49,34 @@ export const CURRENCIES: CurrencyOption[] = [
  * (no minor units) — deal values are tracked to the dollar across
  * the app. `currency` defaults to USD so callers with nothing better
  * stay safe, but pass the account/deal currency wherever known.
+ *
+ * Total by design: `Intl.NumberFormat` throws a RangeError on a
+ * structurally invalid currency code, and `deals.currency` carries
+ * NO DB CHECK (only `accounts.default_currency` does), so legacy
+ * rows, imports, or hand-edited data can hold malformed values like
+ * "United States". We never let that crash a render — on a bad code
+ * we fall back to "CODE 1,234".
  */
 export function formatCurrency(
   value: number,
   currency: string = DEFAULT_CURRENCY,
 ): string {
-  return new Intl.NumberFormat(undefined, {
-    style: "currency",
-    currency: currency || DEFAULT_CURRENCY,
-    minimumFractionDigits: 0,
-    maximumFractionDigits: 0,
-  }).format(Number(value || 0));
+  const code = (currency || DEFAULT_CURRENCY).trim();
+  const amount = Number(value) || 0;
+  try {
+    return new Intl.NumberFormat(undefined, {
+      style: "currency",
+      currency: code,
+      minimumFractionDigits: 0,
+      maximumFractionDigits: 0,
+    }).format(amount);
+  } catch {
+    // Invalid ISO code — show the raw code + grouped number so the
+    // value is still legible instead of throwing.
+    return `${code} ${new Intl.NumberFormat(undefined, {
+      maximumFractionDigits: 0,
+    }).format(amount)}`;
+  }
 }
 
 /**