diff --git a/README.md b/README.md
index dd042d73..7ca3fdfe 100644
--- a/README.md
+++ b/README.md
@@ -127,7 +127,7 @@ const stringify = fastJson(mySchema, {
 ```
 
 - `schema`: external schemas references by $ref property. [More details](#ref)
-- `ajv`: [ajv v8 instance's settings](https://ajv.js.org/options.html) for those properties that require `ajv`. [More details](#anyof)
+- `ajv`: [ajv v8 instance's settings](https://ajv.js.org/options.html) for those properties that require `ajv`. [More details](#anyof) Schema strictness defaults to `false`; pass `ajv: { strictSchema: true }` to reject unknown schema keywords or `ajv: { strictSchema: 'log' }` to log warnings. This applies only to schema paths compiled by Ajv, not to every schema processed by fast-json-stringify.
 - `rounding`: setup how the `integer` types will be rounded when not integers. [More details](#integer)
 - `maxDepth`: maximum number of nested schema levels allowed during compilation.
 Defaults to `100` and may be set from `0` to `100`. Schemas that exceed this limit
diff --git a/lib/validator.js b/lib/validator.js
index 124b5d59..57e053e3 100644
--- a/lib/validator.js
+++ b/lib/validator.js
@@ -15,7 +15,7 @@ class Validator {
     this.ajv = new Ajv({
       ...ajvOptions,
       ...codeOptions,
-      strictSchema: false,
+      strictSchema: ajvOptions?.strictSchema ?? false,
       validateSchema: false,
       allowUnionTypes: true,
       uriResolver: fastUri
diff --git a/test/strict-schema.test.js b/test/strict-schema.test.js
new file mode 100644
index 00000000..0c69f65f
--- /dev/null
+++ b/test/strict-schema.test.js
@@ -0,0 +1,55 @@
+'use strict'
+
+const { test } = require('node:test')
+const build = require('..')
+
+function schemaWithTypo () {
+  return { anyOf: [{ type: 'number', mininum: 10 }] }
+}
+
+for (const compileValidators of [false, true]) {
+  const mode = compileValidators ? 'eager' : 'lazy'
+
+  for (const [name, ajv] of [
+    ['omitted', undefined],
+    ['empty', {}],
+    ['undefined', { strictSchema: undefined }],
+    ['null', { strictSchema: null }],
+    ['false', { strictSchema: false }],
+    ['strict true', { strict: true }],
+    ['explicit false with strict true', { strict: true, strictSchema: false }]
+  ]) {
+    test(`strictSchema keeps permissive behavior for ${name} (${mode})`, t => {
+      const stringify = build(schemaWithTypo(), { ajv, compileValidators })
+      t.assert.equal(stringify(1), '1')
+    })
+  }
+
+  test(`strictSchema true rejects unknown keywords (${mode})`, t => {
+    const options = { ajv: { strictSchema: true }, compileValidators }
+    const unknownKeyword = /unknown keyword: "mininum"/
+
+    if (compileValidators) {
+      t.assert.throws(() => build(schemaWithTypo(), options), unknownKeyword)
+    } else {
+      const stringify = build(schemaWithTypo(), options)
+      t.assert.throws(() => stringify(1), unknownKeyword)
+    }
+  })
+
+  test(`strictSchema log warns about unknown keywords (${mode})`, t => {
+    const warnings = []
+    const logger = {
+      log () {},
+      error () {},
+      warn (message) { warnings.push(message) }
+    }
+    const stringify = build(schemaWithTypo(), {
+      ajv: { strictSchema: 'log', logger },
+      compileValidators
+    })
+
+    t.assert.equal(stringify(1), '1')
+    t.assert.ok(warnings.some(message => message.includes('unknown keyword: "mininum"')))
+  })
+}