diff --git a/lib/iterative/prime.js b/lib/iterative/prime.js
index e92df80..84fce62 100644
--- a/lib/iterative/prime.js
+++ b/lib/iterative/prime.js
@@ -33,7 +33,7 @@ function prime(number) {
   // is less or equals increment
   while (sqrt >= i) {
     // and is divisible by it
-    if (++i % number === 0) {
+    if (number % i++ === 0) {
       return false; // is not a prime number
     }
   }
diff --git a/lib/iterative/test/prime-test.js b/lib/iterative/test/prime-test.js
index 8776008..0491d65 100644
--- a/lib/iterative/test/prime-test.js
+++ b/lib/iterative/test/prime-test.js
@@ -5,6 +5,7 @@ test('prime(number)', function (t) {
   t.equal(prime(0), false, 'should be equal false');
   t.equal(prime(1), false, 'should be equal false');
   t.equal(prime(2), true, 'should be equal true');
+  t.equal(prime(4), false, 'should be equal false');
   t.equal([2, 13, 2017].every(prime), true, 'should be equal true');
   t.end();
 });
diff --git a/package.json b/package.json
index 6f3930a..bb8c30a 100644
--- a/package.json
+++ b/package.json
@@ -23,5 +23,10 @@
     "nyc": "^10.1.2",
     "tap-spec": "^4.1.1",
     "tape": "^4.6.3"
+  },
+  "nyc": {
+    "exclude": [
+      "lib/**/*-test.js"
+    ]
   }
 }