diff --git a/Dotenv.php b/Dotenv.php
index ba56003..6c30803 100644
--- a/Dotenv.php
+++ b/Dotenv.php
@@ -71,7 +71,7 @@ public function setProdEnvs(array $prodEnvs): self
      *
      * @return $this
      */
-    public function usePutenv($usePutenv = true): self
+    public function usePutenv(bool $usePutenv = true): self
     {
         $this->usePutenv = $usePutenv;
 
@@ -190,7 +190,7 @@ public function populate(array $values, bool $overrideExistingVars = false): voi
         $loadedVars = array_flip(explode(',', $_SERVER['SYMFONY_DOTENV_VARS'] ?? $_ENV['SYMFONY_DOTENV_VARS'] ?? ''));
 
         foreach ($values as $name => $value) {
-            $notHttpName = 0 !== strpos($name, 'HTTP_');
+            $notHttpName = !str_starts_with($name, 'HTTP_');
             // don't check existence with getenv() because of thread safety issues
             if (!isset($loadedVars[$name]) && (!$overrideExistingVars && (isset($_ENV[$name]) || (isset($_SERVER[$name]) && $notHttpName)))) {
                 continue;
@@ -427,7 +427,7 @@ private function skipEmptyLines()
 
     private function resolveCommands(string $value, array $loadedVars): string
     {
-        if (false === strpos($value, '$')) {
+        if (!str_contains($value, '$')) {
             return $value;
         }
 
@@ -463,7 +463,7 @@ private function resolveCommands(string $value, array $loadedVars): string
 
             $env = [];
             foreach ($this->values as $name => $value) {
-                if (isset($loadedVars[$name]) || (!isset($_ENV[$name]) && !(isset($_SERVER[$name]) && 0 !== strpos($name, 'HTTP_')))) {
+                if (isset($loadedVars[$name]) || (!isset($_ENV[$name]) && !(isset($_SERVER[$name]) && !str_starts_with($name, 'HTTP_')))) {
                     $env[$name] = $value;
                 }
             }
@@ -481,7 +481,7 @@ private function resolveCommands(string $value, array $loadedVars): string
 
     private function resolveVariables(string $value, array $loadedVars): string
     {
-        if (false === strpos($value, '$')) {
+        if (!str_contains($value, '$')) {
             return $value;
         }
 
@@ -516,7 +516,7 @@ private function resolveVariables(string $value, array $loadedVars): string
                 $value = $this->values[$name];
             } elseif (isset($_ENV[$name])) {
                 $value = $_ENV[$name];
-            } elseif (isset($_SERVER[$name]) && 0 !== strpos($name, 'HTTP_')) {
+            } elseif (isset($_SERVER[$name]) && !str_starts_with($name, 'HTTP_')) {
                 $value = $_SERVER[$name];
             } elseif (isset($this->values[$name])) {
                 $value = $this->values[$name];
diff --git a/composer.json b/composer.json
index de8ec15..6e85c9f 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,8 @@
     ],
     "require": {
         "php": ">=7.2.5",
-        "symfony/deprecation-contracts": "^2.1"
+        "symfony/deprecation-contracts": "^2.1",
+        "symfony/polyfill-php80": "^1.16"
     },
     "require-dev": {
         "symfony/process": "^4.4|^5.0"