diff --git a/src/scripts.js b/src/scripts.js
index a442c47..ee317bb 100644
--- a/src/scripts.js
+++ b/src/scripts.js
@@ -136,31 +136,30 @@ function isMultisigOutput() {
   if (this.chunks < 4) return false
   if (this.chunks[this.chunks.length - 1] !== opcodes.OP_CHECKMULTISIG) return false
 
-  var mS = this.chunks[0]
-  if (!isSmallIntOp(mS)) return false
+  var mOp = this.chunks[0]
+  if (mOp === opcodes.OP_0) return false
+  if (mOp < opcodes.OP_1) return false
+  if (mOp > opcodes.OP_16) return false
 
-  var nS = this.chunks[this.chunks.length - 2]
-  if (!isSmallIntOp(nS)) return false
+  var nOp = this.chunks[this.chunks.length - 2]
+  if (nOp === opcodes.OP_0) return false
+  if (nOp < opcodes.OP_1) return false
+  if (nOp > opcodes.OP_16) return false
 
-  var m = mS - (opcodes.OP_1 - 1)
-  var n = nS - (opcodes.OP_1 - 1)
+  var m = mOp - (opcodes.OP_1 - 1)
+  var n = nOp - (opcodes.OP_1 - 1)
   if (n < m) return false
-  if (n === 0) return false
-  if (m > (this.chunks.length - 3)) return false
 
-  return this.chunks.slice(1, -2).every(isCanonicalPubKey)
+  var pubKeys = this.chunks.slice(1, -2)
+  if (n < pubKeys.length) return false
+
+  return pubKeys.every(isCanonicalPubKey)
 }
 
 function isNulldataOutput() {
   return this.chunks[0] === opcodes.OP_RETURN
 }
 
-function isSmallIntOp(opcode) {
-  if (Buffer.isBuffer(opcode)) return false
-
-  return ((opcode === opcodes.OP_0) || ((opcode >= opcodes.OP_1) && (opcode <= opcodes.OP_16)))
-}
-
 // Standard Script Templates
 // {pubKey} OP_CHECKSIG
 function pubKeyOutput(pubKey) {
diff --git a/test/fixtures/scripts.json b/test/fixtures/scripts.json
index 3728e6e..666ea59 100644
--- a/test/fixtures/scripts.json
+++ b/test/fixtures/scripts.json
@@ -51,6 +51,32 @@
     }
   ],
   "invalid": {
+    "classify": [
+      {
+        "description": "multisig output : m > n",
+        "scriptPubKey": "OP_2 0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 02b80011a883a0fd621ad46dfc405df1e74bf075cbaf700fd4aebef6e96f848340 OP_1 OP_CHECKMULTISIG"
+      },
+      {
+        "description": "multisig output : n === 0",
+        "scriptPubKey": "OP_0 0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 02b80011a883a0fd621ad46dfc405df1e74bf075cbaf700fd4aebef6e96f848340 OP_0 OP_CHECKMULTISIG"
+      },
+      {
+        "description": "multisig output : not (m <= len(pubKeys) <= n)",
+        "scriptPubKey": "OP_2 0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 02b80011a883a0fd621ad46dfc405df1e74bf075cbaf700fd4aebef6e96f848340 024289801366bcee6172b771cf5a7f13aaecd237a0b9a1ff9d769cabc2e6b70a34 OP_2 OP_CHECKMULTISIG"
+      },
+      {
+        "description": "multisig output : m not a small int",
+        "scriptPubKey": "OP_HASH160 024289801366bcee6172b771cf5a7f13aaecd237a0b9a1ff9d769cabc2e6b70a34 OP_1 OP_CHECKMULTISIG"
+      },
+      {
+        "description": "multisig output : n not a small int",
+        "scriptPubKey": "OP_1 024289801366bcee6172b771cf5a7f13aaecd237a0b9a1ff9d769cabc2e6b70a34 OP_HASH160 OP_CHECKMULTISIG"
+      },
+      {
+        "description": "multisig output : non-canonical pubKey (bad length)",
+        "scriptPubKey": "OP_1 0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ffff OP_1 OP_CHECKMULTISIG"
+      }
+    ],
     "multisig": [
       {
         "exception": "Not enough pubKeys provided",
diff --git a/test/scripts.js b/test/scripts.js
index 7376206..b50ec3a 100644
--- a/test/scripts.js
+++ b/test/scripts.js
@@ -32,6 +32,15 @@ describe('Scripts', function() {
         assert.equal(type, f.type)
       })
     })
+
+    fixtures.invalid.classify.forEach(function(f) {
+      it('returns nonstandard for ' + f.description, function() {
+        var script = Script.fromASM(f.scriptPubKey)
+        var type = scripts.classifyOutput(script)
+
+        assert.equal(type, 'nonstandard')
+      })
+    })
   })
 
   describe('pubKey', function() {