diff --git a/ApiCore-Backend/src/automation/number-format.spec.ts b/ApiCore-Backend/src/automation/number-format.spec.ts
index 23665f3..f122531 100644
--- a/ApiCore-Backend/src/automation/number-format.spec.ts
+++ b/ApiCore-Backend/src/automation/number-format.spec.ts
@@ -28,4 +28,11 @@ describe('formatGeneratedNumber', () => {
 
     expect(result).toBe('FIXED-NUMBER');
   });
+
+  it('clamps a pathologically large {SEQ:N} width instead of allocating it', () => {
+    const result = formatGeneratedNumber('L-{SEQ:999999999}', 7, date);
+
+    expect(result).toBe(`L-${'0'.repeat(19)}7`);
+    expect(result.length).toBe(22);
+  });
 });
diff --git a/ApiCore-Backend/src/automation/number-format.ts b/ApiCore-Backend/src/automation/number-format.ts
index a916819..a041b10 100644
--- a/ApiCore-Backend/src/automation/number-format.ts
+++ b/ApiCore-Backend/src/automation/number-format.ts
@@ -1,3 +1,10 @@
+// Far beyond any realistic business use (sequence numbers are a handful of
+// digits) but small enough that padStart can never be tricked into
+// allocating a pathologically large string - {SEQ:999999999} in a
+// carelessly typed format would otherwise try to build a ~1GB string on
+// every single batch/bottling creation from then on.
+const MAX_SEQUENCE_PAD_WIDTH = 20;
+
 // Placeholders: {YYYY} 4-digit year, {YY} 2-digit year, {MM} month (01-12),
 // {DD} day (01-31), {SEQ} running sequence unpadded, {SEQ:N} sequence
 // zero-padded to N digits. Example matching the lastenheft's own sample
@@ -18,7 +25,10 @@ export function formatGeneratedNumber(
     .replace(/\{MM\}/g, mm)
     .replace(/\{DD\}/g, dd)
     .replace(/\{SEQ:(\d+)\}/g, (_match, width: string) =>
-      String(sequence).padStart(Number(width), '0'),
+      String(sequence).padStart(
+        Math.min(Number(width), MAX_SEQUENCE_PAD_WIDTH),
+        '0',
+      ),
     )
     .replace(/\{SEQ\}/g, String(sequence));
 }
diff --git a/ApiCore-Frontend/src/lib/automation/number-format.ts b/ApiCore-Frontend/src/lib/automation/number-format.ts
index 351da39..332c2e2 100644
--- a/ApiCore-Frontend/src/lib/automation/number-format.ts
+++ b/ApiCore-Frontend/src/lib/automation/number-format.ts
@@ -4,6 +4,11 @@
 // Placeholders: {YYYY} 4-digit year, {YY} 2-digit year, {MM} month (01-12),
 // {DD} day (01-31), {SEQ} running sequence unpadded, {SEQ:N} sequence
 // zero-padded to N digits.
+// Same cap as the backend: without it, typing {SEQ:999999999} while
+// editing the format would try to build a multi-hundred-MB string on
+// every keystroke and freeze the settings page.
+const MAX_SEQUENCE_PAD_WIDTH = 20;
+
 export function formatGeneratedNumber(format: string, sequence: number, date: Date): string {
   const yyyy = String(date.getFullYear());
   const yy = yyyy.slice(-2);
@@ -15,6 +20,8 @@ export function formatGeneratedNumber(format: string, sequence: number, date: Da
     .replace(/\{YY\}/g, yy)
     .replace(/\{MM\}/g, mm)
     .replace(/\{DD\}/g, dd)
-    .replace(/\{SEQ:(\d+)\}/g, (_match, width: string) => String(sequence).padStart(Number(width), "0"))
+    .replace(/\{SEQ:(\d+)\}/g, (_match, width: string) =>
+      String(sequence).padStart(Math.min(Number(width), MAX_SEQUENCE_PAD_WIDTH), "0"),
+    )
     .replace(/\{SEQ\}/g, String(sequence));
 }