diff --git a/index.js b/index.js
index 20f2f92..3f94ae7 100644
--- a/index.js
+++ b/index.js
@@ -116,12 +116,13 @@ const getToleranceFromOpts = (opts) => {
 };
 
 const prepareOpts = (opts) => {
-    opts.tolerance = getToleranceFromOpts(opts);
+    const tolerance = getToleranceFromOpts(opts);
 
-    return _.defaults(opts, {
+    return _.defaults({}, opts, {
         ignoreCaret: true,
         ignoreAntialiasing: true,
-        antialiasingTolerance: 0
+        antialiasingTolerance: 0,
+        tolerance: tolerance
     });
 };
 
@@ -228,11 +229,7 @@ exports.createDiff = function saveDiff(opts, callback) {
 };
 
 exports.colors = (color1, color2, opts) => {
-    opts = opts || {};
-
-    if (opts.tolerance === undefined) {
-        opts.tolerance = JND;
-    }
+    opts = _.defaults({}, opts, {tolerance: JND});
 
     const comparator = makeCIEDE2000Comparator(opts.tolerance);
 
diff --git a/test/test.js b/test/test.js
index d9740ae..fac0aef 100644
--- a/test/test.js
+++ b/test/test.js
@@ -62,6 +62,15 @@ describe('looksSame', () => {
         });
     });
 
+    it('should not modify input options', (done) => {
+        const opts = {};
+
+        looksSame(srcPath('ref.png'), srcPath('same.png'), opts, () => {
+            expect(Object.keys(opts)).to.deep.equal([]);
+            done();
+        });
+    });
+
     forFilesAndBuffers((getImage) => {
         it('should return true for similar images', (done) => {
             looksSame(getImage('ref.png'), getImage('same.png'), (error, {equal}) => {
@@ -398,6 +407,24 @@ describe('createDiff', () => {
         }).to.throw(TypeError);
     });
 
+    it('should not modify input options', (done) => {
+        const opts = {
+            reference: srcPath('ref.png'),
+            current: srcPath('same.png'),
+            diff: this.tempName,
+            highlightColor: '#ff00ff'
+        };
+
+        looksSame.createDiff(opts, () => {
+            expect(Object.keys(opts)).to.deep.equal(
+                ['reference', 'current', 'diff', 'highlightColor']
+            );
+            done();
+        });
+
+        // If we got here, the call didn't attempt to modify opts
+    });
+
     it('should format images', (done) => {
         sandbox.spy(utils, 'formatImages');
 
@@ -762,6 +789,17 @@ describe('createDiff', () => {
 });
 
 describe('colors', () => {
+    it('should not modify input options', () => {
+        const opts = {};
+
+        looksSame.colors(
+            {R: 255, G: 0, B: 0},
+            {R: 255, G: 0, B: 0},
+            opts);
+
+        expect(Object.keys(opts)).to.deep.equal([]);
+    });
+
     it('should return true for same colors', () => {
         expect(
             looksSame.colors(