diff --git a/lib/collections.js b/lib/collections.js
index 901a0d7..477e527 100644
--- a/lib/collections.js
+++ b/lib/collections.js
@@ -72,7 +72,7 @@
 
     Iterable.prototype.walk = function(iter) {
       return this.map(function(i) {
-        if ((i.walk != null) && type(i.walk) === "function") {
+        if (type(i != null ? i.walk : void 0) === "function") {
           return i.walk(iter);
         } else {
           return iter(i);
@@ -339,7 +339,7 @@
 
     Map.prototype.walk = function(iter) {
       return this.map(function(v, k) {
-        if (type(v.walk) === "function") {
+        if (type(v != null ? v.walk : void 0) === "function") {
           return iter(v.walk(iter), k);
         } else {
           return iter(v, k);
diff --git a/src/collections.coffee b/src/collections.coffee
index bff2770..4b43166 100644
--- a/src/collections.coffee
+++ b/src/collections.coffee
@@ -27,7 +27,7 @@ class Iterable extends Prim
 
 	walk: (iter) -> 
 		@map (i) -> 
-			if i.walk? and type(i.walk) is "function" 
+			if type(i?.walk) is "function"
 				i.walk iter
 			else
 				iter i
@@ -158,7 +158,7 @@ class Map
 
 	walk: (iter) -> 
 		@map (v, k) ->  	
-			if type(v.walk) is "function"
+			if type(v?.walk) is "function"
 				iter (v.walk iter), k
 			else
 				iter v, k