diff --git a/NEWS b/NEWS
index 2e1ed8a2fda..d1327afee9a 100644
--- a/NEWS
+++ b/NEWS
@@ -14,6 +14,9 @@ PHP                                                                        NEWS
   . Fixed date_sunrise() and date_sunset() with partial-hour UTC offset.
     (ilutov)
 
+- FPM:
+  . Fixed failed debug assertion when php_admin_value setting fails. (ilutov)
+
 - OpenSSL:
   . Fixed bug GH-19245 (Success error message on TLS stream accept failure).
     (Jakub Zelenka)
diff --git a/sapi/fpm/fpm/fpm_php.c b/sapi/fpm/fpm/fpm_php.c
index 2463f4351b6..544188f2159 100644
--- a/sapi/fpm/fpm/fpm_php.c
+++ b/sapi/fpm/fpm/fpm_php.c
@@ -41,6 +41,8 @@ static int fpm_php_zend_ini_alter_master(char *name, int name_length, char *new_
 			ini_entry->modifiable = mode;
 		}
 	} else {
+		/* The string wasn't installed and won't be shared, it's safe to drop. */
+		GC_MAKE_PERSISTENT_LOCAL(duplicate);
 		zend_string_release_ex(duplicate, 1);
 	}
 
diff --git a/sapi/fpm/tests/php_admin_value-failure.phpt b/sapi/fpm/tests/php_admin_value-failure.phpt
new file mode 100644
index 00000000000..dcac2e29c72
--- /dev/null
+++ b/sapi/fpm/tests/php_admin_value-failure.phpt
@@ -0,0 +1,48 @@
+--TEST--
+RC violation on failed php_admin_value
+--SKIPIF--
+<?php include "skipif.inc"; ?>
+--FILE--
+<?php
+
+require_once "tester.inc";
+
+$cfg = <<<EOT
+[global]
+error_log = {{FILE:LOG}}
+[unconfined]
+listen = {{ADDR}}
+pm = dynamic
+pm.max_children = 5
+pm.start_servers = 1
+pm.min_spare_servers = 1
+pm.max_spare_servers = 3
+php_admin_value[precision]=-2
+EOT;
+
+$code = <<<EOT
+<?php
+var_dump(ini_get('precision'));
+EOT;
+
+$ini = <<<EOT
+precision=14
+EOT;
+
+$tester = new FPM\Tester($cfg, $code);
+$tester->setUserIni($ini);
+$tester->start();
+$tester->expectLogStartNotices();
+$tester->request()->expectBody(['string(2) "14"']);
+$tester->terminate();
+$tester->close();
+
+?>
+Done
+--EXPECT--
+Done
+--CLEAN--
+<?php
+require_once "tester.inc";
+FPM\Tester::clean();
+?>