diff --git a/NEWS b/NEWS
index 75d6d1f09f7..77c1e32ff3a 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.5.0beta2
 
+- Core:
+  . Fixed bug GH-18850 (Repeated inclusion of file with __halt_compiler()
+    triggers "Constant already defined" warning). (ilutov)
+
 - ODBC:
   . Remove ODBCVER and assume ODBC 3.5. (Calvin Buckley)
 
diff --git a/Zend/tests/constants/gh18850.inc b/Zend/tests/constants/gh18850.inc
new file mode 100644
index 00000000000..08099278ea3
--- /dev/null
+++ b/Zend/tests/constants/gh18850.inc
@@ -0,0 +1,5 @@
+<?php
+
+var_dump(__COMPILER_HALT_OFFSET__);
+
+__halt_compiler();
diff --git a/Zend/tests/constants/gh18850.phpt b/Zend/tests/constants/gh18850.phpt
new file mode 100644
index 00000000000..7606d50945f
--- /dev/null
+++ b/Zend/tests/constants/gh18850.phpt
@@ -0,0 +1,12 @@
+--TEST--
+GH-18850: Repeated inclusion of file with __halt_compiler() triggers "Constant already defined" warning
+--FILE--
+<?php
+
+require __DIR__ . '/gh18850.inc';
+require __DIR__ . '/gh18850.inc';
+
+?>
+--EXPECT--
+int(62)
+int(62)
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index d8fb26e1776..db611be49ab 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -9752,7 +9752,11 @@ static void zend_compile_halt_compiler(zend_ast *ast) /* {{{ */
 	name = zend_mangle_property_name(const_name, sizeof(const_name) - 1,
 		ZSTR_VAL(filename), ZSTR_LEN(filename), 0);
 
-	zend_register_long_constant(ZSTR_VAL(name), ZSTR_LEN(name), offset, 0, 0);
+	/* Avoid repeated declaration of the __COMPILER_HALT_OFFSET__ constant in
+	 * case this file was already included. */
+	if (!zend_hash_find(EG(zend_constants), name)) {
+		zend_register_long_constant(ZSTR_VAL(name), ZSTR_LEN(name), offset, 0, 0);
+	}
 	zend_string_release_ex(name, 0);
 }
 /* }}} */
diff --git a/ext/phar/tests/bug77432.phpt b/ext/phar/tests/bug77432.phpt
index b3b927a5439..3e3a9988c7d 100644
--- a/ext/phar/tests/bug77432.phpt
+++ b/ext/phar/tests/bug77432.phpt
@@ -38,8 +38,6 @@ include("phar://" . $filename);
 --- Include 1 ---
 hello world
 --- Include 2 ---
-
-Warning: Constant  already defined in %s on line %d
 hello world
 --- After unlink ---