diff --git a/NEWS b/NEWS
index dd28760928e..8f6738078ab 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,7 @@ PHP                                                                        NEWS
 
 - Core:
   . Fixed line number of JMP instruction over else block. (ilutov)
+  . Fixed use-of-uninitialized-value with ??= on assert. (ilutov)
 
 06 Jul 2023, PHP 8.3.0alpha3
 
diff --git a/Zend/tests/gh11580.phpt b/Zend/tests/gh11580.phpt
new file mode 100644
index 00000000000..194c8b5a1aa
--- /dev/null
+++ b/Zend/tests/gh11580.phpt
@@ -0,0 +1,13 @@
+--TEST--
+GH-11580: assert() with ??= operator can lead to use-of-uninitialized-value
+--INI--
+zend.assertions=0
+--FILE--
+<?php
+assert(y)[y] ??= y;
+?>
+--EXPECTF--
+Fatal error: Uncaught Error: Undefined constant "y" in %s:%d
+Stack trace:
+#0 {main}
+  thrown in %s on line %d
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index ea71e075f8c..85f19d32038 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -4203,6 +4203,10 @@ static void zend_compile_assert(znode *result, zend_ast_list *args, zend_string
 		zend_op *opline;
 		uint32_t check_op_number = get_next_op_number();
 
+		/* Assert expression may not be memoized and reused as it may not actually be evaluated. */
+		int orig_memoize_mode = CG(memoize_mode);
+		CG(memoize_mode) = ZEND_MEMOIZE_NONE;
+
 		zend_emit_op(NULL, ZEND_ASSERT_CHECK, NULL, NULL);
 
 		if (fbc && fbc_is_finalized(fbc)) {
@@ -4236,6 +4240,8 @@ static void zend_compile_assert(znode *result, zend_ast_list *args, zend_string
 		opline = &CG(active_op_array)->opcodes[check_op_number];
 		opline->op2.opline_num = get_next_op_number();
 		SET_NODE(opline->result, result);
+
+		CG(memoize_mode) = orig_memoize_mode;
 	} else {
 		if (!fbc) {
 			zend_string_release_ex(name, 0);