diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cace4f34..0655d4cc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -147,6 +147,9 @@ jobs:
         - name: Node.js 25.x
           node-version: "25"
 
+        - name: Node.js 26.x
+          node-version: "26"
+
     steps:
     - uses: actions/checkout@v4
 
diff --git a/HISTORY.md b/HISTORY.md
index e5c4fde6..ed073ba5 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,6 +1,12 @@
+unreleased
+===================
+* fix: improve `limit` option validation (#698)
+  * Invalid `limit` values (e.g. unparseable strings or `NaN`) now throw instead of being silently ignored, which previously disabled size limit enforcement
+  * `null` and `undefined` fall back to the default 100kb limit
+
 1.20.5 / 2026-04-24
 ===================
-* refactor(json): simplify strict mode error string construction 
+* refactor(json): simplify strict mode error string construction
 * fix: extended urlencoded parsing of arrays with >100 elements (#716)
 * deps: qs@~6.15.1
 
diff --git a/lib/types/json.js b/lib/types/json.js
index d1f510d9..f1802434 100644
--- a/lib/types/json.js
+++ b/lib/types/json.js
@@ -53,15 +53,19 @@ var JSON_SYNTAX_REGEXP = /#+/g
 function json (options) {
   var opts = options || {}
 
-  var limit = typeof opts.limit !== 'number'
-    ? bytes.parse(opts.limit || '100kb')
-    : opts.limit
+  var limit = typeof opts.limit === 'undefined' || opts.limit === null
+    ? 102400 // 100kb default
+    : bytes.parse(opts.limit)
   var inflate = opts.inflate !== false
   var reviver = opts.reviver
   var strict = opts.strict !== false
   var type = opts.type || 'application/json'
   var verify = opts.verify || false
 
+  if (limit === null) {
+    throw new TypeError('option limit "' + String(opts.limit) + '" is invalid')
+  }
+
   if (verify !== false && typeof verify !== 'function') {
     throw new TypeError('option verify must be function')
   }
diff --git a/lib/types/raw.js b/lib/types/raw.js
index f5d1b674..2b3e06d7 100644
--- a/lib/types/raw.js
+++ b/lib/types/raw.js
@@ -33,12 +33,16 @@ function raw (options) {
   var opts = options || {}
 
   var inflate = opts.inflate !== false
-  var limit = typeof opts.limit !== 'number'
-    ? bytes.parse(opts.limit || '100kb')
-    : opts.limit
+  var limit = typeof opts.limit === 'undefined' || opts.limit === null
+    ? 102400 // 100kb default
+    : bytes.parse(opts.limit)
   var type = opts.type || 'application/octet-stream'
   var verify = opts.verify || false
 
+  if (limit === null) {
+    throw new TypeError('option limit "' + String(opts.limit) + '" is invalid')
+  }
+
   if (verify !== false && typeof verify !== 'function') {
     throw new TypeError('option verify must be function')
   }
diff --git a/lib/types/text.js b/lib/types/text.js
index 083a0090..5247a925 100644
--- a/lib/types/text.js
+++ b/lib/types/text.js
@@ -35,12 +35,16 @@ function text (options) {
 
   var defaultCharset = opts.defaultCharset || 'utf-8'
   var inflate = opts.inflate !== false
-  var limit = typeof opts.limit !== 'number'
-    ? bytes.parse(opts.limit || '100kb')
-    : opts.limit
+  var limit = typeof opts.limit === 'undefined' || opts.limit === null
+    ? 102400 // 100kb default
+    : bytes.parse(opts.limit)
   var type = opts.type || 'text/plain'
   var verify = opts.verify || false
 
+  if (limit === null) {
+    throw new TypeError('option limit "' + String(opts.limit) + '" is invalid')
+  }
+
   if (verify !== false && typeof verify !== 'function') {
     throw new TypeError('option verify must be function')
   }
diff --git a/lib/types/urlencoded.js b/lib/types/urlencoded.js
index 892e3469..52ebe5f9 100644
--- a/lib/types/urlencoded.js
+++ b/lib/types/urlencoded.js
@@ -50,12 +50,16 @@ function urlencoded (options) {
 
   var extended = opts.extended !== false
   var inflate = opts.inflate !== false
-  var limit = typeof opts.limit !== 'number'
-    ? bytes.parse(opts.limit || '100kb')
-    : opts.limit
+  var limit = typeof opts.limit === 'undefined' || opts.limit === null
+    ? 102400 // 100kb default
+    : bytes.parse(opts.limit)
   var type = opts.type || 'application/x-www-form-urlencoded'
   var verify = opts.verify || false
 
+  if (limit === null) {
+    throw new TypeError('option limit "' + String(opts.limit) + '" is invalid')
+  }
+
   if (verify !== false && typeof verify !== 'function') {
     throw new TypeError('option verify must be function')
   }
diff --git a/test/json.js b/test/json.js
index c76ea138..cca9e223 100644
--- a/test/json.js
+++ b/test/json.js
@@ -130,6 +130,36 @@ describe('bodyParser.json()', function () {
   })
 
   describe('with limit option', function () {
+    it('should throw an error for an invalid string limit', function () {
+      assert.throws(function () {
+        bodyParser.json({ limit: 'invalid' })
+      }, /option limit "invalid" is invalid/)
+      assert.throws(function () {
+        bodyParser.json({ limit: '' })
+      }, /option limit "" is invalid/)
+    })
+
+    it('should throw an error for a NaN limit', function () {
+      assert.throws(function () {
+        bodyParser.json({ limit: NaN })
+      }, /option limit "NaN" is invalid/)
+    })
+
+    it('should throw an error for a boolean limit', function () {
+      assert.throws(function () {
+        bodyParser.json({ limit: true })
+      }, /option limit "true" is invalid/)
+      assert.throws(function () {
+        bodyParser.json({ limit: false })
+      }, /option limit "false" is invalid/)
+    })
+
+    it('should throw an error for an object limit', function () {
+      assert.throws(function () {
+        bodyParser.json({ limit: { foo: 'bar' } })
+      }, /option limit "\[object Object\]" is invalid/)
+    })
+
     it('should 413 when over limit with Content-Length', function (done) {
       var buf = Buffer.alloc(1024, '.')
       request(createServer({ limit: '1kb' }))
diff --git a/test/raw.js b/test/raw.js
index d2ab027f..9cff05e7 100644
--- a/test/raw.js
+++ b/test/raw.js
@@ -88,6 +88,36 @@ describe('bodyParser.raw()', function () {
   })
 
   describe('with limit option', function () {
+    it('should throw an error for an invalid string limit', function () {
+      assert.throws(function () {
+        bodyParser.raw({ limit: 'invalid' })
+      }, /option limit "invalid" is invalid/)
+      assert.throws(function () {
+        bodyParser.raw({ limit: '' })
+      }, /option limit "" is invalid/)
+    })
+
+    it('should throw an error for a NaN limit', function () {
+      assert.throws(function () {
+        bodyParser.raw({ limit: NaN })
+      }, /option limit "NaN" is invalid/)
+    })
+
+    it('should throw an error for a boolean limit', function () {
+      assert.throws(function () {
+        bodyParser.raw({ limit: true })
+      }, /option limit "true" is invalid/)
+      assert.throws(function () {
+        bodyParser.raw({ limit: false })
+      }, /option limit "false" is invalid/)
+    })
+
+    it('should throw an error for an object limit', function () {
+      assert.throws(function () {
+        bodyParser.raw({ limit: { foo: 'bar' } })
+      }, /option limit "\[object Object\]" is invalid/)
+    })
+
     it('should 413 when over limit with Content-Length', function (done) {
       var buf = Buffer.alloc(1028, '.')
       var server = createServer({ limit: '1kb' })
diff --git a/test/text.js b/test/text.js
index c3c55180..e723266b 100644
--- a/test/text.js
+++ b/test/text.js
@@ -106,6 +106,36 @@ describe('bodyParser.text()', function () {
   })
 
   describe('with limit option', function () {
+    it('should throw an error for an invalid string limit', function () {
+      assert.throws(function () {
+        bodyParser.text({ limit: 'invalid' })
+      }, /option limit "invalid" is invalid/)
+      assert.throws(function () {
+        bodyParser.text({ limit: '' })
+      }, /option limit "" is invalid/)
+    })
+
+    it('should throw an error for a NaN limit', function () {
+      assert.throws(function () {
+        bodyParser.text({ limit: NaN })
+      }, /option limit "NaN" is invalid/)
+    })
+
+    it('should throw an error for a boolean limit', function () {
+      assert.throws(function () {
+        bodyParser.text({ limit: true })
+      }, /option limit "true" is invalid/)
+      assert.throws(function () {
+        bodyParser.text({ limit: false })
+      }, /option limit "false" is invalid/)
+    })
+
+    it('should throw an error for an object limit', function () {
+      assert.throws(function () {
+        bodyParser.text({ limit: { foo: 'bar' } })
+      }, /option limit "\[object Object\]" is invalid/)
+    })
+
     it('should 413 when over limit with Content-Length', function (done) {
       var buf = Buffer.alloc(1028, '.')
       request(createServer({ limit: '1kb' }))
diff --git a/test/urlencoded.js b/test/urlencoded.js
index 970c1e12..f8542ae2 100644
--- a/test/urlencoded.js
+++ b/test/urlencoded.js
@@ -323,6 +323,36 @@ describe('bodyParser.urlencoded()', function () {
   })
 
   describe('with limit option', function () {
+    it('should throw an error for an invalid string limit', function () {
+      assert.throws(function () {
+        bodyParser.urlencoded({ limit: 'invalid' })
+      }, /option limit "invalid" is invalid/)
+      assert.throws(function () {
+        bodyParser.urlencoded({ limit: '' })
+      }, /option limit "" is invalid/)
+    })
+
+    it('should throw an error for a NaN limit', function () {
+      assert.throws(function () {
+        bodyParser.urlencoded({ limit: NaN })
+      }, /option limit "NaN" is invalid/)
+    })
+
+    it('should throw an error for a boolean limit', function () {
+      assert.throws(function () {
+        bodyParser.urlencoded({ limit: true })
+      }, /option limit "true" is invalid/)
+      assert.throws(function () {
+        bodyParser.urlencoded({ limit: false })
+      }, /option limit "false" is invalid/)
+    })
+
+    it('should throw an error for an object limit', function () {
+      assert.throws(function () {
+        bodyParser.urlencoded({ limit: { foo: 'bar' } })
+      }, /option limit "\[object Object\]" is invalid/)
+    })
+
     it('should 413 when over limit with Content-Length', function (done) {
       var buf = Buffer.alloc(1024, '.')
       request(createServer({ limit: '1kb' }))