diff --git a/src/Composer/Config.php b/src/Composer/Config.php
index 455ae6db7..4d03a4971 100644
--- a/src/Composer/Config.php
+++ b/src/Composer/Config.php
@@ -211,6 +211,7 @@ class Config
     public function get($key, $flags = 0)
     {
         switch ($key) {
+            // strings/paths with env var and {$refs} support
             case 'vendor-dir':
             case 'bin-dir':
             case 'process-timeout':
@@ -234,20 +235,33 @@ class Config
 
                 return (($flags & self::RELATIVE_PATHS) == self::RELATIVE_PATHS) ? $val : $this->realpath($val);
 
+            // booleans with env var support
             case 'htaccess-protect':
-                $value = $this->getComposerEnv('COMPOSER_HTACCESS_PROTECT');
-                if (false === $value) {
-                    $value = $this->config[$key];
-                }
-                return $value !== 'false' && (bool) $value;
+                // convert foo-bar to COMPOSER_FOO_BAR and check if it exists since it overrides the local config
+                $env = 'COMPOSER_' . strtoupper(strtr($key, '-', '_'));
 
+                $val = $this->getComposerEnv($env);
+                if (false === $val) {
+                    $val = $this->config[$key];
+                }
+                return $val !== 'false' && (bool) $val;
+
+            // booleans without env var support
+            case 'disable-tls':
+            case 'secure-http':
+            case 'use-github-api':
+            case 'lock':
+                return $this->config[$key] !== 'false' && (bool) $this->config[$key];
+
+            // ints without env var support
             case 'cache-ttl':
                 return (int) $this->config[$key];
 
+            // numbers with kb/mb/gb support, without env var support
             case 'cache-files-maxsize':
                 if (!preg_match('/^\s*([0-9.]+)\s*(?:([kmg])(?:i?b)?)?\s*$/i', $this->config[$key], $matches)) {
                     throw new \RuntimeException(
-                        "Could not parse the value of 'cache-files-maxsize': {$this->config[$key]}"
+                        "Could not parse the value of '$key': {$this->config[$key]}"
                     );
                 }
                 $size = $matches[1];
@@ -269,6 +283,7 @@ class Config
 
                 return $size;
 
+            // special cases below
             case 'cache-files-ttl':
                 if (isset($this->config[$key])) {
                     return (int) $this->config[$key];
@@ -326,14 +341,6 @@ class Config
 
                 return $protos;
 
-            case 'disable-tls':
-                return $this->config[$key] !== 'false' && (bool) $this->config[$key];
-            case 'secure-http':
-                return $this->config[$key] !== 'false' && (bool) $this->config[$key];
-            case 'use-github-api':
-                return $this->config[$key] !== 'false' && (bool) $this->config[$key];
-            case 'lock':
-                return $this->config[$key] !== 'false' && (bool) $this->config[$key];
             default:
                 if (!isset($this->config[$key])) {
                     return null;