diff --git a/HISTORY.md b/HISTORY.md
index 432dc206a..776e4f61d 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -10,6 +10,7 @@
   Thanks @johnmarinelli.
 - Fixed #523: In some circumstances, matrix subset returned a scalar instead 
   of the correct subset.
+- Fixed #536: A bug in an internal method used for sparse matrices.
 
 
 ## 2015-12-05, version 2.5.0
diff --git a/lib/function/algebra/sparse/cs_amd.js b/lib/function/algebra/sparse/cs_amd.js
index 3109648dc..60fefbaac 100644
--- a/lib/function/algebra/sparse/cs_amd.js
+++ b/lib/function/algebra/sparse/cs_amd.js
@@ -161,7 +161,7 @@ function factory (type, config, load) {
       // scan, no entry in the w array is greater than or equal to mark.
       
       // clear w if necessary
-      mark = _wclear(mark, lemax, w, n);
+      mark = _wclear(mark, lemax, W, w, n);
       // scan 1: find |Le\Lk|
       for (pk = pk1; pk < pk2; pk++) {
         i = cindex[pk];
@@ -275,7 +275,7 @@ function factory (type, config, load) {
       W[degree + k] = dk;
       lemax = Math.max(lemax, dk);
       // clear w
-      mark = _wclear(mark + lemax, lemax, w, n);
+      mark = _wclear(mark + lemax, lemax, W, w, n);
       
       // Supernode detection. Supernode detection relies on the hash function h(i) computed for each node i.
       // If two nodes have identical adjacency lists, their hash functions wil be identical.
@@ -496,7 +496,7 @@ function factory (type, config, load) {
       W[degree + i] = W[len + i];
     }
     // clear w
-    var mark = _wclear(0, 0, w, n);
+    var mark = _wclear(0, 0, W, w, n);
     // n is a dead element
     W[elen + n] = -2;
     // n is a root of assembly tree
@@ -549,15 +549,15 @@ function factory (type, config, load) {
     return nel;
   };
 
-  var _wclear = function(mark, lemax, w, n) {
+  var _wclear = function(mark, lemax, W, w, n) {
     if (mark < 2 || (mark + lemax < 0)) {
       for (var k = 0; k < n; k++) {
-        if (w[k] !== 0)
-          w[k] = 1;
+        if (W[w + k] !== 0)
+          W[w + k] = 1;
       }
       mark = 2 ;
     }
-    // at this point, w [0..n-1] < mark holds
+    // at this point, W [0..n-1] < mark holds
     return mark;
   };