diff --git a/NEWS b/NEWS
index bf57077f454..409972a1fe9 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,9 @@ PHP                                                                        NEWS
     inaccurate sunrise and sunset times, but other calculated times are
     correct) (JiriJozif).
 
+- Standard:
+  . Fixed bug GH-17403 (Potential deadlock when putenv fails). (nielsdos)
+
 08 May 2025, PHP 8.3.21
 
 - Core:
diff --git a/ext/standard/basic_functions.c b/ext/standard/basic_functions.c
index 99d92af167f..d2a99fccc95 100644
--- a/ext/standard/basic_functions.c
+++ b/ext/standard/basic_functions.c
@@ -849,6 +849,7 @@ PHP_FUNCTION(putenv)
 #endif
 		RETURN_TRUE;
 	} else {
+		tsrm_env_unlock();
 		free(pe.putenv_string);
 		zend_string_release(pe.key);
 #ifdef PHP_WIN32