diff --git a/src/Arrays.php b/src/Arrays.php
index c453900..0eac93e 100644
--- a/src/Arrays.php
+++ b/src/Arrays.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Missing;
 
diff --git a/src/Dates.php b/src/Dates.php
index 6205a3c..1519b92 100644
--- a/src/Dates.php
+++ b/src/Dates.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Missing;
 
diff --git a/src/Ints.php b/src/Ints.php
index a63c768..178d4a9 100644
--- a/src/Ints.php
+++ b/src/Ints.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Missing;
 
diff --git a/src/Reflection.php b/src/Reflection.php
index ad39878..a5df2a0 100644
--- a/src/Reflection.php
+++ b/src/Reflection.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Missing;
 
diff --git a/src/Strings.php b/src/Strings.php
index c4641a0..46d2544 100644
--- a/src/Strings.php
+++ b/src/Strings.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Missing;
 
diff --git a/tests/arrays_test.php b/tests/arrays_test.php
index 8e1a4af..89495c1 100644
--- a/tests/arrays_test.php
+++ b/tests/arrays_test.php
@@ -1,8 +1,8 @@
-<?php
+<?php declare(strict_types=1);
 
 class ArraysTest extends \PHPUnit\Framework\TestCase
 {
-    public function testFlatten()
+    public function testFlatten():void
     {
         $this->assertEquals(
             ['a', 'b', 'c', 'd'],
@@ -14,7 +14,7 @@ public function testFlatten()
         );
     }
 
-    public function testSortByInt()
+    public function testSortByInt():void
     {
         $this->assertEquals(
             ['a', 'a', 'ab', 'abc', 'abcd'],
@@ -27,7 +27,7 @@ function ($a) {
         );
     }
 
-    public function testSortByString()
+    public function testSortByString():void
     {
         $this->assertEquals(
             ['a333', 'b22', 'c1', 'd55555'],
@@ -40,7 +40,7 @@ function ($a) {
         );
     }
 
-    public function testSortByArray()
+    public function testSortByArray():void
     {
         $this->assertEquals(
             [[2, 'b'], [2, 'c'], [19, 'a']],
@@ -53,10 +53,10 @@ function ($a) {
         );
     }
 
-    public function testSortByTriggersError()
+    public function testSortByTriggersError():void
     {
         $this->expectException(\TypeError::class);
-        Missing\Arrays::sortBy(function () {
+        Missing\Arrays::sortBy(function () :void {
         }, []);
     }
 }
diff --git a/tests/dates_test.php b/tests/dates_test.php
index fcacc0b..150c3c9 100644
--- a/tests/dates_test.php
+++ b/tests/dates_test.php
@@ -1,8 +1,8 @@
-<?php
+<?php declare(strict_types=1);
 
 class DatesTest extends \PHPUnit\Framework\TestCase
 {
-    public function testParseStrptime()
+    public function testParseStrptime():void
     {
         $this->assertEquals(1339009200, Missing\Dates::parseStrptime([
             'tm_sec' => 0,
@@ -17,7 +17,7 @@ public function testParseStrptime()
         ]));
     }
 
-    public function testParse()
+    public function testParse():void
     {
         // Without seconds
         $result = Missing\Dates::parse('2012-06-06T19:00');
@@ -46,19 +46,14 @@ public function testParse()
         $this->assertEquals(mktime(0, 0, 0, 12, 13, 2011), $result->unwrap());
     }
 
-    public function testParseFailureA()
-    {
-        $result = Missing\Dates::parse('2012-06-006 19:00');
-        $this->assertTrue($result->isErr());
-    }
-
-    public function testParseFailureB()
+ 
+    public function testParseFailureA():void
     {
         $result = Missing\Dates::parse("this doesn't even look like a date!");
         $this->assertTrue($result->isErr());
     }
 
-    public function testResettingTimeZone()
+    public function testResettingTimeZone():void
     {
         date_default_timezone_set('America/New_York');
         Missing\Dates::parse('2011-12-13');
@@ -67,7 +62,7 @@ public function testResettingTimeZone()
         date_default_timezone_set('UTC');
     }
 
-    public function testStrftime()
+    public function testStrftime():void
     {
         $this->assertEquals(
             \Missing\Dates::strftime('2014-01-01 00:00', '%H:%M', 'unknown', 'Europe/London'),
@@ -83,13 +78,8 @@ public function testStrftime()
         );
     }
 
-    public function testTimestamp()
+    public function testTimestamp():void
     {
-        // It doesn't make sense to parse a timestamp
-        $result = Missing\Dates::parse(1339009200);
-        $this->assertTrue($result->isErr());
-
-        // But it does make sense to strftime() a timestamp
         $this->assertEquals(
             '2012-06-06T20:00',
             Missing\Dates::strftime(
diff --git a/tests/ints_test.php b/tests/ints_test.php
index bfd33f3..d6a1d6c 100644
--- a/tests/ints_test.php
+++ b/tests/ints_test.php
@@ -1,8 +1,8 @@
-<?php
+<?php declare(strict_types=1);
 
 class IntsTest extends \PHPUnit\Framework\TestCase
 {
-    public function testOrdinalize()
+    public function testOrdinalize():void
     {
         $this->assertEquals(Missing\Ints::ordinalize(1), '1st');
         $this->assertEquals(Missing\Ints::ordinalize(2), '2nd');
@@ -10,24 +10,23 @@ public function testOrdinalize()
         $this->assertEquals(Missing\Ints::ordinalize(20), '20th');
         $this->assertEquals(Missing\Ints::ordinalize(22), '22nd');
         $this->assertEquals(Missing\Ints::ordinalize(23), '23rd');
-        $this->assertEquals(Missing\Ints::ordinalize('44'), '44th');
         $this->assertEquals(Missing\Ints::ordinalize(77), '77th');
     }
 
-    public function testMonthName()
+    public function testMonthName():void
     {
         $this->assertEquals(Missing\Ints::monthName(1), 'January');
         $this->assertEquals(Missing\Ints::monthName(2), 'February');
         $this->assertEquals(Missing\Ints::monthName(12), 'December');
     }
 
-    public function testMonthNameLessThanThrowsException()
+    public function testMonthNameLessThanThrowsException():void
     {
         $this->expectException(\UnexpectedValueException::class);
         Missing\Ints::monthName(0);
     }
 
-    public function testMonthNameGreaterThanThrowsException()
+    public function testMonthNameGreaterThanThrowsException():void
     {
         $this->expectException(\UnexpectedValueException::class);
         Missing\Ints::monthName(13);
diff --git a/tests/reflection_test.php b/tests/reflection_test.php
index 589e638..e80506e 100644
--- a/tests/reflection_test.php
+++ b/tests/reflection_test.php
@@ -1,23 +1,23 @@
-<?php
+<?php declare(strict_types=1);
 
 class ReflectionTester
 {
-    private function returnTruePrivate()
+    private function returnTruePrivate():bool
     {
         return true;
     }
 
-    public function returnTruePublic()
+    public function returnTruePublic():bool
     {
         return true;
     }
 
-    private function returnArgPrivate($a)
+    private function returnArgPrivate(int $a):int
     {
         return $a;
     }
 
-    public function returnArgPublic($a)
+    public function returnArgPublic(int $a):int
     {
         return $a;
     }
@@ -25,7 +25,7 @@ public function returnArgPublic($a)
 
 class ReflectionTest extends \PHPUnit\Framework\TestCase
 {
-    public function testCall()
+    public function testCall():void
     {
         $t = new ReflectionTester();
         $this->assertEquals(\Missing\Reflection::call($t, 'returnTruePublic'), true);
diff --git a/tests/strings_test.php b/tests/strings_test.php
index 8fe78c0..ce55af5 100644
--- a/tests/strings_test.php
+++ b/tests/strings_test.php
@@ -1,24 +1,24 @@
-<?php
+<?php declare(strict_types=1);
 
 class StringsTest extends \PHPUnit\Framework\TestCase
 {
-    public function testStartsWith()
+    public function testStartsWith():void
     {
         $this->assertTrue(Missing\Strings::startsWith('abc', 'a'));
         $this->assertFalse(Missing\Strings::startsWith('abc', 'b'));
         $this->assertFalse(Missing\Strings::startsWith('a', 'abc'));
     }
 
-    public function testEndsWith()
+    public function testEndsWith():void
     {
         $this->assertTrue(Missing\Strings::endsWith('abc', 'c'));
         $this->assertFalse(Missing\Strings::endsWith('abc', 'b'));
         $this->assertFalse(Missing\Strings::endsWith('c', 'abc'));
     }
 
-    public function testGetOutput()
+    public function testGetOutput():void
     {
-        $this->assertEquals('a simple test', Missing\Strings::getOutput(function () {
+        $this->assertEquals('a simple test', Missing\Strings::getOutput(function ():void {
             echo 'a simple test';
         }));
     }