diff --git a/src/evaluate.js b/src/evaluate.js
index e45fbf7..1b57b80 100644
--- a/src/evaluate.js
+++ b/src/evaluate.js
@@ -33,9 +33,9 @@ module.exports = function (cacheKey, nurbs, accessors, debug, checkBounds, isBas
       if (derivative[i] === undefined) derivative[i] = 0;
       totalDerivativeOrder += derivative[i];
     }
-    if (hasWeights && totalDerivativeOrder > 1) {
-      throw new Error('Analytical derivative not implemented for rational b-splines with order n = ' + totalDerivativeOrder + '.');
-    }
+    //if (hasWeights && totalDerivativeOrder > 1) {
+      //throw new Error('Analytical derivative not implemented for rational b-splines with order n = ' + totalDerivativeOrder + '.');
+    //}
   }
 
   if (isBasis) cacheKey = 'Basis' + cacheKey;
@@ -101,9 +101,9 @@ module.exports = function (cacheKey, nurbs, accessors, debug, checkBounds, isBas
   function debugLine (str) {
     if (debug) line(str);
   }
-  // function clog (str) {
-    // if (debug) code.push('console.log("' + str + ' =", ' + str + ');');
-  // }
+  //function clog (str) {
+    //if (debug) code.push('console.log("' + str + ' =", ' + str + ');');
+  //}
 
   if (isBasis) {
     var indexArgs = [];
@@ -300,6 +300,10 @@ module.exports = function (cacheKey, nurbs, accessors, debug, checkBounds, isBas
     for (i = 0; i < degree[d]; i++) {
       debugLine('\n  // Degree ' + degree[d] + ' evaluation in dimension ' + d + ', step ' + (i + 1) + '\n');
       for (j = degree[d]; j > i; j--) {
+        /*if (derivative) {
+          console.log('derivative, degree[d], i:', derivative, degree[d], i);
+          console.log('degree[d] - i - derivative[d]:', degree[d] - i - derivative[d]);
+        }*/
         var isDerivative = derivative && (degree[d] - i - derivative[d] <= 0);
 
         if (isDerivative) {
@@ -343,7 +347,11 @@ module.exports = function (cacheKey, nurbs, accessors, debug, checkBounds, isBas
               var ij1WithDimension = ij1.slice();
               for (m = 0; m < spaceDimension; m++) {
                 ijWithDimension[splineDimension] = ij1WithDimension[splineDimension] = m;
-                weightFactor = hasWeights ? 'h * ' + weightVar(ij1) + ' / ' + weightVar(ij) + ' * ' : '';
+                //if (i === degree[d] - 1) {
+                  //weightFactor = hasWeights ? 'h * ' + weightVar(ij1) + ' / (' + weightVar(ij) + ' * '+weightVar(ij)+') * ' : '';
+                //} else {
+                  weightFactor = hasWeights ? 'h * ' + weightVar(ij1) + ' / ' + weightVar(ij) +' * ' : '';
+                //}
                 pt1 = pointVar(ijWithDimension) + (hasWeights ? ' / h' : '');
                 pt2 = pointVar(ij1WithDimension) + (hasWeights ? ' / ' + weightVar(ij1) : '');
                 line(pointVar(ijWithDimension) + ' = ' + derivCoeff + ' * ' + weightFactor + '(' + pt1 + ' - ' + pt2 + ') * m;');
diff --git a/test/derivative.js b/test/derivative.js
index 4e5d7cb..8b35d2f 100644
--- a/test/derivative.js
+++ b/test/derivative.js
@@ -381,4 +381,55 @@ test('array-of-array style nurbs', function (t) {
       t.end();
     });
   });
+  
+  t.test('second derivative of NURBS curves', function (t) {
+    t.test('of a quartic b-spline', function (t) {
+      var deg = 4;
+      var points = [[0], [1], [4], [2], [4], [6], [8]];
+      var spline = nurbs({
+        points: points,
+        knots: [new Array(points.length + deg + 1).fill(0).map((d, i) => Math.sqrt(2 + i))],
+        //weights: new Array(points.length).fill(0).map((d, i) => Math.pow(i + 1, 2)),
+        degree: deg,
+      });
+
+      var der1 = spline.evaluator([1]);
+      var der2 = spline.evaluator([2]);
+      var der3 = spline.evaluator([3]);
+      var der4 = spline.evaluator([4]);
+      var domain = spline.domain[0];
+      var samples = 3;
+
+      var h = 1e-3;
+
+      for (var i = 0; i < samples; i++) {
+        var u = domain[0] + (domain[1] - domain[0]) * (i + 1) / (samples + 1);
+
+        var ym2 = spline.evaluate([], u - 2 * h)[0];
+        var ym = spline.evaluate([], u - h)[0];
+        var y0 = spline.evaluate([], u)[0];
+        var yp = spline.evaluate([], u + h)[0];
+        var yp2 = spline.evaluate([], u + 2 * h)[0];
+
+        var expectedDer1 = (yp - ym) / (2 * h);
+        var actualDer1 = der1([], u)[0];
+
+        var expectedDer2 = (yp - 2 * y0 + ym) / (h * h);
+        var actualDer2 = der2([], u)[0];
+
+        var expectedDer3 = ((yp2 - ym2) - 2 * (yp - ym)) / 2 / (h * h * h);
+        var actualDer3 = der3([], u)[0];
+
+        var expectedDer4 = (ym2 + yp2 - 4 * (yp + ym) + 6 * y0) / (h * h * h * h);
+        var actualDer4 = der4([], u)[0];
+
+        t.ok(almostEqual(actualDer1, expectedDer1, 2e-3), 'first derivative at t = ' + u + ', expected: ' + expectedDer1 + ', actual: ' + actualDer1);
+        t.ok(almostEqual(actualDer2, expectedDer2, 2e-3), 'second derivative at t = ' + u + ', expected: ' + expectedDer2 + ', actual: ' + actualDer2);
+        t.ok(almostEqual(actualDer3, expectedDer3, 2e-3), 'third derivative at t = ' + u + ', expected: ' + expectedDer3 + ', actual: ' + actualDer3);
+        t.ok(almostEqual(actualDer4, expectedDer4, 2e-3), 'fourth derivative at t = ' + u + ', expected: ' + expectedDer4 + ', actual: ' + actualDer4);
+      }
+
+      t.end();
+    });
+  });
 });