diff --git a/lib/bcoin/script.js b/lib/bcoin/script.js
index ac520449..b5d83760 100644
--- a/lib/bcoin/script.js
+++ b/lib/bcoin/script.js
@@ -1082,8 +1082,9 @@ script.isPubkeyhash = function isPubkeyhash(s, hash) {
   return true;
 };
 
-script.isMultisig = function isMultisig(s, pubs) {
-  var m, n, keys, total;
+script.isMultisig = function isMultisig(s, keys) {
+  var m, n, i, j;
+  var total = 0;
 
   s = script.subscript(s);
 
@@ -1093,43 +1094,52 @@ script.isMultisig = function isMultisig(s, pubs) {
   if (s.length < 4)
     return false;
 
-  // compat
-  if (pubs && !utils.isBuffer(pubs[0]))
-    pubs = [pubs];
-
-  m = s[0];
-  if (typeof m === 'number' && m >= 1 && m <= 15)
-    m = [m];
-  if (!Array.isArray(m) || m.length !== 1)
-    return false;
-  m = m[0] || 0;
-
   if (s[s.length - 1] !== 'checkmultisig')
     return false;
 
-  n = s[s.length - 2];
-  if (typeof n === 'number' && n >= 1 && n <= 15)
-    n = [n];
-  if (!Array.isArray(n) || n.length !== 1)
+  m = s[0];
+
+  if (Array.isArray(m)) {
+    if (m.length !== 1)
+      return false;
+    m = m[0];
+  }
+
+  if (!(m >= 1 && m <= 15))
+    return false;
+
+  n = s[s.length - 2];
+
+  if (Array.isArray(n)) {
+    if (n.length !== 1)
+      return false;
+    n = n[0];
+  }
+
+  if (!(n >= m && n <= 15))
     return false;
-  n = n[0] || 0;
 
   if (n + 3 !== s.length)
     return false;
 
-  keys = s.slice(1, 1 + n);
+  for (i = 1; i < n + 1; i++) {
+    if (!Array.isArray(s[i]))
+      return false;
+  }
 
-  if (!keys.every(Array.isArray))
-    return false;
-
-  if (!pubs)
+  if (!keys)
     return true;
 
-  total = keys.filter(function(k) {
-    return pubs.some(function(pub) {
-      return utils.isEqual(k, pub);
-    });
-  }).length;
+  keys = utils.sortKeys(keys);
+
+  for (i = 1; i < n + 1; i++) {
+    for (j = 0; j < keys.length; j++) {
+      if (utils.isEqual(s[i], keys[j])) {
+        total++;
+        break;
+      }
+    }
+  }
 
   return total === n;
 };
@@ -1199,8 +1209,11 @@ script.isPubkeyInput = function isPubkeyInput(s, key, tx, i) {
   // Execute the script against our key's
   // checksig script to see if this is our input.
   // This will only work if the script verifies.
-  if (key)
+  if (key) {
+    assert(tx);
+    assert(i != null);
     return script.verify(s, [key, 'checksig'], tx, i);
+  }
 
   return true;
 };
@@ -1247,7 +1260,10 @@ script.isMultisigInput = function isMultisigInput(s, keys, tx, i) {
   // Execute the script against our pubkeys'
   // redeem script to see if this is our input.
   // This will only work if the script verifies.
-  if (keys && keys.length >= 2) {
+  if (keys) {
+    assert(keys.length >= 2);
+    assert(tx);
+    assert(i != null);
     o = script.redeem(keys, s.length - 1, keys.length);
     return script.verify(s, o, tx, i);
   }
diff --git a/lib/bcoin/utils.js b/lib/bcoin/utils.js
index 40a2d684..e08edbe8 100644
--- a/lib/bcoin/utils.js
+++ b/lib/bcoin/utils.js
@@ -754,7 +754,7 @@ utils.hidden = function hidden(obj, prop, value) {
 };
 
 utils.sortKeys = function sortKeys(keys) {
-  return keys.sort(function(a, b) {
+  return keys.slice().sort(function(a, b) {
     return new bn(a).cmp(new bn(b)) > 0;
   });
 };