diff --git a/NEWS b/NEWS
index 0d9e42792078..5bbabbf66dc8 100644
--- a/NEWS
+++ b/NEWS
@@ -5,6 +5,8 @@ PHP                                                                        NEWS
 - Core:
   . Fixed bug GH-15375 (Nested "yield from" skips items after a valid() or
     next() call on the inner generator). (iliaal)
+  . Fixed bug GH-23232 (is_callable('\::method') asks the autoloader for an
+    empty class name). (spawnia)
 
 27 Aug 2026, PHP 8.4.25
 
diff --git a/Zend/tests/gh23232.phpt b/Zend/tests/gh23232.phpt
new file mode 100644
index 000000000000..d32baa8b071a
--- /dev/null
+++ b/Zend/tests/gh23232.phpt
@@ -0,0 +1,27 @@
+--TEST--
+GH-23232 (is_callable('\::method') asks the autoloader for an empty class name)
+--FILE--
+<?php
+spl_autoload_register(function (string $class): void {
+    echo "autoload: '$class'\n";
+});
+
+foreach (['::a', '\::a', '\Foo::a', 'Foo::a'] as $callable) {
+    echo "is_callable(\"$callable\")\n";
+    var_dump(is_callable($callable));
+}
+
+var_dump(class_exists('\\'));
+?>
+--EXPECT--
+is_callable("::a")
+bool(false)
+is_callable("\::a")
+bool(false)
+is_callable("\Foo::a")
+autoload: 'Foo'
+bool(false)
+is_callable("Foo::a")
+autoload: 'Foo'
+bool(false)
+bool(false)
diff --git a/Zend/zend_execute_API.c b/Zend/zend_execute_API.c
index c81a8cfe5ff7..6e42be5f888c 100644
--- a/Zend/zend_execute_API.c
+++ b/Zend/zend_execute_API.c
@@ -1180,6 +1180,10 @@ ZEND_API zend_class_entry *zend_lookup_class_ex(zend_string *name, zend_string *
 		}
 
 		if (ZSTR_VAL(name)[0] == '\\') {
+			if (ZSTR_LEN(name) == 1) {
+				/* A lone namespace separator names no class, e.g. is_callable('\::method'). */
+				return NULL;
+			}
 			lc_name = zend_string_alloc(ZSTR_LEN(name) - 1, 0);
 			zend_str_tolower_copy(ZSTR_VAL(lc_name), ZSTR_VAL(name) + 1, ZSTR_LEN(name) - 1);
 		} else {