diff --git a/lib/os/class.ISPConfigDebian10OS.inc.php b/lib/os/class.ISPConfigDebian10OS.inc.php
index 2c0d4a3a4634f0ffe29b06dfde43a13600fcbcba..3320219197290de7ed9f82793bbab415bb24ab9b 100644
--- a/lib/os/class.ISPConfigDebian10OS.inc.php
+++ b/lib/os/class.ISPConfigDebian10OS.inc.php
@@ -57,7 +57,12 @@ class ISPConfigDebian10OS extends ISPConfigDebianOS {
 		}
 
 		if(ISPConfig::shallInstall('web')) {
-			$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.3 ; update-alternatives --set php-fpm.sock /run/php/php7.3-fpm.sock';
+			// When --use-php-system is used, there is no alternative for php-fpm.sock.
+			if(ISPConfig::wantsPHP() === 'system') {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.3';
+			} else {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.3 ; update-alternatives --set php-fpm.sock /run/php/php7.3-fpm.sock';
+			}
 			$result = $this->exec($cmd);
 			if($result === false) {
 				throw new ISPConfigOSException('Command ' . $cmd . ' failed.');
diff --git a/lib/os/class.ISPConfigDebianOS.inc.php b/lib/os/class.ISPConfigDebianOS.inc.php
index ccaa6e97b3eb3119c4727f20b43ae37903c99b92..7d8b53d36dc76702bbcc0a996f21f5ab5ed2df45 100644
--- a/lib/os/class.ISPConfigDebianOS.inc.php
+++ b/lib/os/class.ISPConfigDebianOS.inc.php
@@ -182,7 +182,12 @@ class ISPConfigDebianOS extends ISPConfigBaseOS {
 		}
 
 		if(ISPConfig::shallInstall('web')) {
-			$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.0 ; update-alternatives --set php-fpm.sock /run/php/php7.0-fpm.sock';
+			// When --use-php-system is used, there is no alternative for php-fpm.sock.
+			if(ISPConfig::wantsPHP() === 'system') {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.0';
+			} else {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.0 ; update-alternatives --set php-fpm.sock /run/php/php7.0-fpm.sock';
+			}
 			$result = $this->exec($cmd);
 			if($result === false) {
 				throw new ISPConfigOSException('Command ' . $cmd . ' failed.');
diff --git a/lib/os/class.ISPConfigUbuntu2004OS.inc.php b/lib/os/class.ISPConfigUbuntu2004OS.inc.php
index 8f1d91dbe0bebb83cf7c74898ddd9acc6a458a3f..8d647fdf1fce548ff73cff72ee9c785ad99d822e 100644
--- a/lib/os/class.ISPConfigUbuntu2004OS.inc.php
+++ b/lib/os/class.ISPConfigUbuntu2004OS.inc.php
@@ -107,7 +107,12 @@ maxretry = 3';
 		}
 
 		if(ISPConfig::shallInstall('web')) {
-			$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.4 ; update-alternatives --set php-fpm.sock /run/php/php7.4-fpm.sock';
+			// When --use-php-system is used, there is no alternative for php-fpm.sock.
+			if(ISPConfig::wantsPHP() === 'system') {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.4';
+			} else {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.4 ; update-alternatives --set php-fpm.sock /run/php/php7.4-fpm.sock';
+			}
 			$result = $this->exec($cmd);
 			if($result === false) {
 				throw new ISPConfigOSException('Command ' . $cmd . ' failed.');
diff --git a/lib/os/class.ISPConfigUbuntuOS.inc.php b/lib/os/class.ISPConfigUbuntuOS.inc.php
index 51614b8c1ffcf6fc347d33c705a834bdbdd46e28..b40a4625c0d51091f6914908219b3323a8c8cf72 100644
--- a/lib/os/class.ISPConfigUbuntuOS.inc.php
+++ b/lib/os/class.ISPConfigUbuntuOS.inc.php
@@ -90,7 +90,12 @@ maxretry = 3';
 		}
 
 		if(ISPConfig::shallInstall('web')) {
-			$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.2 ; update-alternatives --set php-fpm.sock /run/php/php7.2-fpm.sock';
+			// When --use-php-system is used, there is no alternative for php-fpm.sock.
+			if(ISPConfig::wantsPHP() === 'system') {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.2';
+			} else {
+				$cmd = 'update-alternatives --set php-cgi /usr/bin/php-cgi7.2 ; update-alternatives --set php-fpm.sock /run/php/php7.2-fpm.sock';
+			}
 			$result = $this->exec($cmd);
 			if($result === false) {
 				throw new ISPConfigOSException('Command ' . $cmd . ' failed.');