diff --git a/resources/schema.json b/resources/schema.json
index 2abac35b6..35efdd2e5 100644
--- a/resources/schema.json
+++ b/resources/schema.json
@@ -357,6 +357,7 @@
                 "UnwrapStrShuffle": { "$ref": "#/definitions/default-mutator-config" },
                 "UnwrapStrToLower": { "$ref": "#/definitions/default-mutator-config" },
                 "UnwrapStrToUpper": { "$ref": "#/definitions/default-mutator-config" },
+                "UnwrapSubstr": { "$ref": "#/definitions/default-mutator-config" },
                 "UnwrapTrim": { "$ref": "#/definitions/default-mutator-config" },
                 "UnwrapUcFirst": { "$ref": "#/definitions/default-mutator-config" },
                 "UnwrapUcWords": { "$ref": "#/definitions/default-mutator-config" },
diff --git a/src/Mutator/ProfileList.php b/src/Mutator/ProfileList.php
index a0b2af87a..6d1669d6f 100644
--- a/src/Mutator/ProfileList.php
+++ b/src/Mutator/ProfileList.php
@@ -247,6 +247,7 @@ final class ProfileList
         Mutator\Unwrap\UnwrapStrShuffle::class,
         Mutator\Unwrap\UnwrapStrToLower::class,
         Mutator\Unwrap\UnwrapStrToUpper::class,
+        Mutator\Unwrap\UnwrapSubstr::class,
         Mutator\Unwrap\UnwrapTrim::class,
         Mutator\Unwrap\UnwrapUcFirst::class,
         Mutator\Unwrap\UnwrapUcWords::class,
@@ -433,6 +434,7 @@ final class ProfileList
         'UnwrapStrShuffle' => Mutator\Unwrap\UnwrapStrShuffle::class,
         'UnwrapStrToLower' => Mutator\Unwrap\UnwrapStrToLower::class,
         'UnwrapStrToUpper' => Mutator\Unwrap\UnwrapStrToUpper::class,
+        'UnwrapSubstr' => Mutator\Unwrap\UnwrapSubstr::class,
         'UnwrapTrim' => Mutator\Unwrap\UnwrapTrim::class,
         'UnwrapUcFirst' => Mutator\Unwrap\UnwrapUcFirst::class,
         'UnwrapUcWords' => Mutator\Unwrap\UnwrapUcWords::class,
diff --git a/src/Mutator/Unwrap/UnwrapSubstr.php b/src/Mutator/Unwrap/UnwrapSubstr.php
new file mode 100644
index 000000000..cd576b02e
--- /dev/null
+++ b/src/Mutator/Unwrap/UnwrapSubstr.php
@@ -0,0 +1,72 @@
+<?php
+/**
+ * This code is licensed under the BSD 3-Clause License.
+ *
+ * Copyright (c) 2017, Maks Rafalko
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name of the copyright holder nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+declare(strict_types=1);
+
+namespace Infection\Mutator\Unwrap;
+
+use Infection\Mutator\Definition;
+use Infection\Mutator\MutatorCategory;
+
+/**
+ * @internal
+ */
+final class UnwrapSubstr extends AbstractUnwrapMutator
+{
+    public static function getDefinition(): ?Definition
+    {
+        return new Definition(
+            <<<'TXT'
+Replaces a `substr` function call with its first operand. For example:
+
+```php
+$x = substr('abcde', 0, -1);
+```
+
+Will be mutated to:
+
+```php
+$x = 'abcde';
+```
+TXT
+            ,
+            MutatorCategory::SEMANTIC_REDUCTION,
+            null
+        );
+    }
+
+    protected function getFunctionName(): string
+    {
+        return 'substr';
+    }
+}
diff --git a/tests/phpunit/Mutator/Unwrap/UnwrapSubstrTest.php b/tests/phpunit/Mutator/Unwrap/UnwrapSubstrTest.php
new file mode 100644
index 000000000..d929d5ca5
--- /dev/null
+++ b/tests/phpunit/Mutator/Unwrap/UnwrapSubstrTest.php
@@ -0,0 +1,191 @@
+<?php
+/**
+ * This code is licensed under the BSD 3-Clause License.
+ *
+ * Copyright (c) 2017, Maks Rafalko
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name of the copyright holder nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+declare(strict_types=1);
+
+namespace Infection\Tests\Mutator\Unwrap;
+
+use Infection\Tests\Mutator\BaseMutatorTestCase;
+
+final class UnwrapSubstrTest extends BaseMutatorTestCase
+{
+    /**
+     * @dataProvider mutationsProvider
+     *
+     * @param string|string[] $expected
+     */
+    public function test_it_can_mutate(string $input, $expected = []): void
+    {
+        $this->doTest($input, $expected);
+    }
+
+    public function mutationsProvider(): iterable
+    {
+        yield 'It mutates correctly when provided with a string' => [
+            <<<'PHP'
+<?php
+
+$a = substr('Good Afternoon!', 0, -1);
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = 'Good Afternoon!';
+PHP
+        ];
+
+        yield 'It mutates correctly when provided with a constant' => [
+            <<<'PHP'
+<?php
+
+$a = substr(\Class_With_Const::Const, 0, -1);
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = \Class_With_Const::Const;
+PHP
+        ];
+
+        yield 'It mutates correctly when a backslash is in front of str_replace' => [
+            <<<'PHP'
+<?php
+
+$a = \substr('Good Afternoon!', 0, -1);
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = 'Good Afternoon!';
+PHP
+        ];
+
+        yield 'It mutates correctly within if statements' => [
+            <<<'PHP'
+<?php
+
+$a = 'Good Afternoon!';
+if (substr($a, 0, -1) === $a) {
+    return true;
+}
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = 'Good Afternoon!';
+if ($a === $a) {
+    return true;
+}
+PHP
+        ];
+
+        yield 'It mutates correctly when sUbStR is wrongly capitalized' => [
+            <<<'PHP'
+<?php
+
+$a = sUbStR('Good Afternoon!', 0, -1);
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = 'Good Afternoon!';
+PHP
+        ];
+
+        yield 'It mutates correctly when substr uses another function as input' => [
+            <<<'PHP'
+<?php
+
+$a = substr($foo->bar(), 0, -1);
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = $foo->bar();
+PHP
+        ];
+
+        yield 'It mutates correctly when provided with a more complex situation' => [
+            <<<'PHP'
+<?php
+
+$a = substr(array_reduce($words, function (string $carry, string $item) {
+    return $carry;
+}), 0, -1);
+PHP
+            ,
+            <<<'PHP'
+<?php
+
+$a = array_reduce($words, function (string $carry, string $item) {
+    return $carry;
+});
+PHP
+        ];
+
+        yield 'It does not mutate other str* calls' => [
+            <<<'PHP'
+<?php
+
+$a = strrev('Afternoon');
+PHP
+        ];
+
+        yield 'It does not mutate functions named str_replace' => [
+            <<<'PHP'
+<?php
+
+function substr($search , $replace , $subject , int &$count = null)
+{
+}
+PHP
+        ];
+
+        yield 'It does not break when provided with a variable function name' => [
+            <<<'PHP'
+<?php
+
+$a = 'substr';
+
+$b = $a('Bar', 0, -1);
+PHP
+            ,
+        ];
+    }
+}