diff --git a/NEWS b/NEWS
index a9ccb65c10b..97144036d35 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,9 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.5.0alpha2
 
+- Core:
+  . Fix OSS-Fuzz #427814452 (pipe compilation fails with assert). (nielsdos)
+
 - DOM:
   . Make cloning DOM node lists, maps, and collections fail. (nielsdos)
 
diff --git a/Zend/tests/pipe_operator/gh18965.phpt b/Zend/tests/pipe_operator/gh18965.phpt
new file mode 100644
index 00000000000..8f9eaaebb08
--- /dev/null
+++ b/Zend/tests/pipe_operator/gh18965.phpt
@@ -0,0 +1,12 @@
+--TEST--
+GH-18965: ASSERT_CHECK avoids pipe lhs free
+--INI--
+zend.assertions=0
+--FILE--
+<?php
+namespace Foo;
+range(0, 10) |> assert(...);
+echo "No leak\n";
+?>
+--EXPECT--
+No leak
diff --git a/Zend/tests/pipe_operator/oss_fuzz_427814452.phpt b/Zend/tests/pipe_operator/oss_fuzz_427814452.phpt
new file mode 100644
index 00000000000..2ecfbab6348
--- /dev/null
+++ b/Zend/tests/pipe_operator/oss_fuzz_427814452.phpt
@@ -0,0 +1,26 @@
+--TEST--
+OSS-Fuzz #427814452
+--FILE--
+<?php
+
+try {
+    false |> assert(...);
+} catch (\AssertionError $e) {
+    echo $e::class, ": '", $e->getMessage(), "'\n";
+}
+try {
+    0 |> "assert"(...);
+} catch (\AssertionError $e) {
+    echo $e::class, ": '", $e->getMessage(), "'\n";
+}
+try {
+    false |> ("a"."ssert")(...);
+} catch (\AssertionError $e) {
+    echo $e::class, ": '", $e->getMessage(), "'\n";
+}
+
+?>
+--EXPECT--
+AssertionError: ''
+AssertionError: ''
+AssertionError: ''
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index f3f6d1b75ae..ef167efc697 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -6426,6 +6426,20 @@ static bool can_match_use_jumptable(zend_ast_list *arms) {
 	return 1;
 }
 
+static bool zend_is_pipe_optimizable_callable_name(zend_ast *ast)
+{
+	if (ast->kind == ZEND_AST_ZVAL && Z_TYPE_P(zend_ast_get_zval(ast)) == IS_STRING) {
+		/* Assert compilation adds a message operand, but this is incompatible with the
+		 * pipe optimization that uses a temporary znode for the reference elimination.
+		 * Therefore, disable the optimization for assert.
+		 * Note that "assert" as a name is always treated as fully qualified. */
+		zend_string *str = zend_ast_get_str(ast);
+		return !zend_string_equals_literal_ci(str, "assert");
+	}
+
+	return true;
+}
+
 static void zend_compile_pipe(znode *result, zend_ast *ast)
 {
 	zend_ast *operand_ast = ast->child[0];
@@ -6453,7 +6467,8 @@ static void zend_compile_pipe(znode *result, zend_ast *ast)
 
 	/* Turn $foo |> bar(...) into bar($foo). */
 	if (callable_ast->kind == ZEND_AST_CALL
-		&& callable_ast->child[1]->kind == ZEND_AST_CALLABLE_CONVERT) {
+		&& callable_ast->child[1]->kind == ZEND_AST_CALLABLE_CONVERT
+		&& zend_is_pipe_optimizable_callable_name(callable_ast->child[0])) {
 		fcall_ast = zend_ast_create(ZEND_AST_CALL,
 				callable_ast->child[0], arg_list_ast);
 	/* Turn $foo |> bar::baz(...) into bar::baz($foo). */