diff --git a/extensions/memory-lancedb/index.test.ts b/extensions/memory-lancedb/index.test.ts
index 98ca81ae71a..b2ed4920bb9 100644
--- a/extensions/memory-lancedb/index.test.ts
+++ b/extensions/memory-lancedb/index.test.ts
@@ -2408,6 +2408,7 @@ describe("memory plugin e2e", () => {
     const customTooLong = `I always prefer this style. ${"x".repeat(1600)}`;
     expect(shouldCapture(customAllowed, { maxChars: 1500 })).toBe(true);
     expect(shouldCapture(customTooLong, { maxChars: 1500 })).toBe(false);
+    expect(shouldCapture(defaultTooLong, { maxChars: Number.NaN })).toBe(false);
   });
 
   test("normalizeRecallQuery trims whitespace and bounds embedding input", () => {
@@ -2415,6 +2416,7 @@ describe("memory plugin e2e", () => {
       "remember the blue mug",
     );
     expect(normalizeRecallQuery(`look up ${"x".repeat(200)}`, 120)).toHaveLength(120);
+    expect(normalizeRecallQuery(`look up ${"x".repeat(2000)}`, Number.NaN)).toHaveLength(1000);
   });
 
   test("normalizeEmbeddingVector accepts float arrays and base64 float32 responses", () => {
diff --git a/extensions/memory-lancedb/index.ts b/extensions/memory-lancedb/index.ts
index a084767b3f5..dd12ccf1d0f 100644
--- a/extensions/memory-lancedb/index.ts
+++ b/extensions/memory-lancedb/index.ts
@@ -139,10 +139,16 @@ export function normalizeRecallQuery(
   maxChars: number = DEFAULT_RECALL_MAX_CHARS,
 ): string {
   const normalized = text.replace(/\s+/g, " ").trim();
-  const limit = Math.max(0, Math.floor(maxChars));
+  const limit = normalizeMaxChars(maxChars, DEFAULT_RECALL_MAX_CHARS);
   return normalized.length > limit ? truncateUtf16Safe(normalized, limit).trimEnd() : normalized;
 }
 
+function normalizeMaxChars(value: number | undefined, fallback: number): number {
+  return typeof value === "number" && Number.isFinite(value)
+    ? Math.max(0, Math.floor(value))
+    : fallback;
+}
+
 function messageFingerprint(message: unknown): string {
   const msgObj = asRecord(message);
   if (!msgObj) {
@@ -572,7 +578,7 @@ export function shouldCapture(
   text: string,
   options?: { customTriggers?: string[]; maxChars?: number },
 ): boolean {
-  const maxChars = options?.maxChars ?? DEFAULT_CAPTURE_MAX_CHARS;
+  const maxChars = normalizeMaxChars(options?.maxChars, DEFAULT_CAPTURE_MAX_CHARS);
   if (text.length > maxChars) {
     return false;
   }