diff --git a/index.js b/index.js
index 924976a1..601ccd78 100755
--- a/index.js
+++ b/index.js
@@ -317,7 +317,18 @@ module.exports.interpolator = {
   vertexSplitQuadraticBasisSpline: 'vsqbs'
 };
 Sharp.prototype.interpolateWith = function(interpolator) {
-  this.options.interpolator = interpolator;
+  var isValid = false;
+  for (var key in module.exports.interpolator) {
+    if (module.exports.interpolator[key] === interpolator) {
+      isValid = true;
+      break;
+    }
+  }
+  if (isValid) {
+    this.options.interpolator = interpolator;
+  } else {
+    throw new Error('Invalid interpolator ' + interpolator);
+  }
   return this;
 };
 
diff --git a/test/unit/interpolation.js b/test/unit/interpolation.js
index 732fc44f..6349b149 100755
--- a/test/unit/interpolation.js
+++ b/test/unit/interpolation.js
@@ -94,15 +94,13 @@ describe('Interpolation', function() {
   });
 
   it('unknown interpolator throws', function(done) {
-    sharp(fixtures.inputJpg)
-      .resize(320, 240)
-      .interpolateWith('nonexistant')
-      .toBuffer()
-      .catch(function (e) {
-        assert(
-          e.toString().match(/VipsInterpolate: class "nonexistant" not found/)
-        );
-      })
-      .finally(done);
+    var isValid = false;
+    try {
+      sharp().interpolateWith('nonexistant');
+      isValid = true;
+    } catch (e) {}
+    assert(!isValid);
+    done();
   });
+
 });
diff --git a/test/unit/normalize.js b/test/unit/normalize.js
index 4d96781e..73a85ba3 100755
--- a/test/unit/normalize.js
+++ b/test/unit/normalize.js
@@ -34,7 +34,7 @@ describe('Normalization', function () {
     sharp(fixtures.inputJpgWithLowContrast)
       .gamma()
       .greyscale()
-      .normalize()
+      .normalize(true)
       .raw()
       .toBuffer(function (err, data, info) {
         if (err) throw err;