diff --git a/Zend/zend_vm_def.h b/Zend/zend_vm_def.h
index df255c5a868f..1bfb4986f7f5 100644
--- a/Zend/zend_vm_def.h
+++ b/Zend/zend_vm_def.h
@@ -4014,7 +4014,12 @@ ZEND_VM_HOT_HANDLER(61, ZEND_INIT_FCALL, NUM, CONST, NUM|CACHE_SLOT)
 	if (UNEXPECTED(fbc == NULL)) {
 		fname = (zval*)RT_CONSTANT(opline, opline->op2);
 		func = zend_hash_find_known_hash(EG(function_table), Z_STR_P(fname));
-		ZEND_ASSERT(func != NULL && "Function existence must be checked at compile time");
+		/* The function table can differ from the one the script was compiled with.
+		 * A call compiled for an internal function (op2.extra is its offset) can't go to a user function. */
+		if (UNEXPECTED(func == NULL)
+		 || (Z_EXTRA_P(fname) && UNEXPECTED(Z_FUNC_P(func)->type != ZEND_INTERNAL_FUNCTION))) {
+			ZEND_VM_DISPATCH_TO_HELPER(zend_undefined_function_helper);
+		}
 		fbc = Z_FUNC_P(func);
 		if (EXPECTED(fbc->type == ZEND_USER_FUNCTION) && UNEXPECTED(!RUN_TIME_CACHE(&fbc->op_array))) {
 			init_func_run_time_cache(&fbc->op_array);
@@ -4038,7 +4043,22 @@ ZEND_VM_HOT_TYPE_SPEC_HANDLER(ZEND_INIT_FCALL, Z_EXTRA_P(RT_CONSTANT(op, op->op2
 	zend_execute_data *call;
 	fbc = CACHED_PTR(opline->result.num);
 	if (UNEXPECTED(fbc == NULL)) {
-		fbc = Z_PTR(EG(function_table)->arData[Z_EXTRA_P(RT_CONSTANT(opline, opline->op2))].val);
+		zval *fname = (zval*)RT_CONSTANT(opline, opline->op2);
+		uint32_t offset = Z_EXTRA_P(fname);
+		Bucket *p = EG(function_table)->arData;
+
+		/* The offset is stale if the function table differs from the one the script was compiled with. */
+		if (EXPECTED(offset < EG(function_table)->nNumUsed)
+		 && EXPECTED(p[offset].key && zend_string_equals(p[offset].key, Z_STR_P(fname)))) {
+			fbc = Z_PTR(p[offset].val);
+		} else {
+			zval *func = zend_hash_find_known_hash(EG(function_table), Z_STR_P(fname));
+			fbc = func ? Z_FUNC_P(func) : NULL;
+		}
+		/* The call was compiled for an internal function and can't go to a user function. */
+		if (UNEXPECTED(fbc == NULL) || UNEXPECTED(fbc->type != ZEND_INTERNAL_FUNCTION)) {
+			ZEND_VM_DISPATCH_TO_HELPER(zend_undefined_function_helper);
+		}
 		CACHE_PTR(opline->result.num, fbc);
 	}
 	call = _zend_vm_stack_push_call_frame_ex(
diff --git a/Zend/zend_vm_execute.h b/Zend/zend_vm_execute.h
index 4b313f20cd39..aff93d3a31dc 100644
--- a/Zend/zend_vm_execute.h
+++ b/Zend/zend_vm_execute.h
@@ -4031,7 +4031,12 @@ static ZEND_VM_HOT ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL ZEND_INIT_FCALL_SPEC_CO
 	if (UNEXPECTED(fbc == NULL)) {
 		fname = (zval*)RT_CONSTANT(opline, opline->op2);
 		func = zend_hash_find_known_hash(EG(function_table), Z_STR_P(fname));
-		ZEND_ASSERT(func != NULL && "Function existence must be checked at compile time");
+		/* The function table can differ from the one the script was compiled with.
+		 * A call compiled for an internal function (op2.extra is its offset) can't go to a user function. */
+		if (UNEXPECTED(func == NULL)
+		 || (Z_EXTRA_P(fname) && UNEXPECTED(Z_FUNC_P(func)->type != ZEND_INTERNAL_FUNCTION))) {
+			ZEND_VM_TAIL_CALL(zend_undefined_function_helper_SPEC(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU));
+		}
 		fbc = Z_FUNC_P(func);
 		if (EXPECTED(fbc->type == ZEND_USER_FUNCTION) && UNEXPECTED(!RUN_TIME_CACHE(&fbc->op_array))) {
 			init_func_run_time_cache(&fbc->op_array);
@@ -4055,7 +4060,22 @@ static ZEND_VM_HOT ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL ZEND_INIT_FCALL_OFFSET_
 	zend_execute_data *call;
 	fbc = CACHED_PTR(opline->result.num);
 	if (UNEXPECTED(fbc == NULL)) {
-		fbc = Z_PTR(EG(function_table)->arData[Z_EXTRA_P(RT_CONSTANT(opline, opline->op2))].val);
+		zval *fname = (zval*)RT_CONSTANT(opline, opline->op2);
+		uint32_t offset = Z_EXTRA_P(fname);
+		Bucket *p = EG(function_table)->arData;
+
+		/* The offset is stale if the function table differs from the one the script was compiled with. */
+		if (EXPECTED(offset < EG(function_table)->nNumUsed)
+		 && EXPECTED(p[offset].key && zend_string_equals(p[offset].key, Z_STR_P(fname)))) {
+			fbc = Z_PTR(p[offset].val);
+		} else {
+			zval *func = zend_hash_find_known_hash(EG(function_table), Z_STR_P(fname));
+			fbc = func ? Z_FUNC_P(func) : NULL;
+		}
+		/* The call was compiled for an internal function and can't go to a user function. */
+		if (UNEXPECTED(fbc == NULL) || UNEXPECTED(fbc->type != ZEND_INTERNAL_FUNCTION)) {
+			ZEND_VM_TAIL_CALL(zend_undefined_function_helper_SPEC(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU));
+		}
 		CACHE_PTR(opline->result.num, fbc);
 	}
 	call = _zend_vm_stack_push_call_frame_ex(
diff --git a/ext/opcache/tests/gh24661.phpt b/ext/opcache/tests/gh24661.phpt
new file mode 100644
index 000000000000..97984fb378bf
--- /dev/null
+++ b/ext/opcache/tests/gh24661.phpt
@@ -0,0 +1,101 @@
+--TEST--
+GH-24661 (Wrong function called or crash if the function table changed)
+--EXTENSIONS--
+opcache
+--SKIPIF--
+<?php
+$dl_test = PHP_OS_FAMILY === 'Windows' ? 'php_dl_test.dll' : 'dl_test.so';
+if (!file_exists(ini_get('extension_dir') . DIRECTORY_SEPARATOR . $dl_test)) {
+    die('skip dl_test extension is not built');
+}
+?>
+--FILE--
+<?php
+$cache = __DIR__ . DIRECTORY_SEPARATOR . 'gh24661';
+$script = $cache . DIRECTORY_SEPARATOR . 'main.php';
+mkdir($cache);
+file_put_contents($script, <<<'PHP'
+<?php
+if (($argv[1] ?? '') === 'dl') {
+    dl('dl_test');
+} elseif (($argv[1] ?? '') === 'user') {
+    include __DIR__ . '/user.php';
+}
+include __DIR__ . '/call.php';
+PHP);
+file_put_contents($cache . DIRECTORY_SEPARATOR . 'user.php', <<<'PHP'
+<?php
+function dl_test_test2(string $str = ''): string {
+    return "User $str";
+}
+PHP);
+/* call.php is compiled after dl(). The try/catch keeps the call in f() from being
+ * specialized to ZEND_INIT_FCALL_OFFSET. Both calls are compiled for the internal
+ * function and must not go to a user function of the same name. */
+file_put_contents($cache . DIRECTORY_SEPARATOR . 'call.php', <<<'PHP'
+<?php
+set_exception_handler(function (Throwable $e) {
+    echo $e::class, ": ", $e->getMessage(), "\n";
+});
+function f() {
+    try {
+        return dl_test_test2('f');
+    } catch (Error $e) {
+        return $e::class . ": " . $e->getMessage();
+    }
+}
+echo f(), "\n";
+echo dl_test_test2('main'), "\n";
+PHP);
+
+function run(string $cache, array $args): void {
+    $ext = ini_get('extension_dir');
+    $opcache = PHP_OS_FAMILY === 'Windows' ? 'php_opcache.dll' : 'opcache.so';
+    $cmd = [PHP_BINARY, '-n', '-d', 'extension_dir="' . $ext . '"'];
+    if (file_exists($ext . DIRECTORY_SEPARATOR . $opcache)) {
+        array_push($cmd, '-d', 'zend_extension=opcache');
+    }
+    array_push($cmd,
+        '-d', 'opcache.enable_cli=1',
+        '-d', 'opcache.file_cache="' . $cache . '"',
+        '-d', 'opcache.file_cache_only=1',
+        '-d', 'opcache.file_update_protection=0',
+        ...$args,
+    );
+    $proc = proc_open($cmd, [1 => ['pipe', 'w'], 2 => ['pipe', 'w']], $pipes);
+    echo stream_get_contents($pipes[1]);
+    stream_get_contents($pipes[2]);
+    proc_close($proc);
+}
+
+echo "--- Compiled with dl_test loaded ---\n";
+run($cache, [$script, 'dl']);
+echo "--- Cached, run without dl_test ---\n";
+run($cache, [$script]);
+echo "--- Cached, run with a user function of the same name ---\n";
+run($cache, [$script, 'user']);
+?>
+--CLEAN--
+<?php
+$cache = __DIR__ . DIRECTORY_SEPARATOR . 'gh24661';
+if (is_dir($cache)) {
+    $it = new RecursiveIteratorIterator(
+        new RecursiveDirectoryIterator($cache, FilesystemIterator::SKIP_DOTS),
+        RecursiveIteratorIterator::CHILD_FIRST
+    );
+    foreach ($it as $file) {
+        $file->isDir() ? rmdir($file->getPathname()) : unlink($file->getPathname());
+    }
+    rmdir($cache);
+}
+?>
+--EXPECT--
+--- Compiled with dl_test loaded ---
+Hello f
+Hello main
+--- Cached, run without dl_test ---
+Error: Call to undefined function dl_test_test2()
+Error: Call to undefined function dl_test_test2()
+--- Cached, run with a user function of the same name ---
+Error: Call to undefined function dl_test_test2()
+Error: Call to undefined function dl_test_test2()
diff --git a/sapi/fpm/tests/gh24661-opcache-pools-disable-functions.phpt b/sapi/fpm/tests/gh24661-opcache-pools-disable-functions.phpt
new file mode 100644
index 000000000000..c3321742282f
--- /dev/null
+++ b/sapi/fpm/tests/gh24661-opcache-pools-disable-functions.phpt
@@ -0,0 +1,77 @@
+--TEST--
+FPM: GH-24661 - Script cached by a pool with other disable_functions calls the wrong function
+--EXTENSIONS--
+opcache
+--SKIPIF--
+<?php include "skipif.inc"; ?>
+--FILE--
+<?php
+
+require_once "tester.inc";
+
+$cfg = <<<EOT
+[global]
+error_log = {{FILE:LOG}}
+[unrestricted]
+listen = {{ADDR[unrestricted]}}
+pm = static
+pm.max_children = 1
+[restricted]
+listen = {{ADDR[restricted]}}
+pm = static
+pm.max_children = 1
+php_admin_value[disable_functions] = getmypid
+EOT;
+
+/* Disabling getmypid() moves var_export() in the function table. The try/catch
+ * keeps the calls in f() from being specialized to ZEND_INIT_FCALL_OFFSET. */
+$code = <<<'EOT'
+<?php
+set_exception_handler(function (Throwable $e) {
+    echo $e->getMessage(), "\n";
+});
+function f() {
+    try {
+        return gettype(getmypid());
+    } catch (Error $e) {
+        return $e->getMessage();
+    }
+}
+echo f(), "\n";
+echo var_export(true, true), "\n";
+echo gettype(getmypid()), "\n";
+EOT;
+
+$expected = [
+    'unrestricted' => ['integer', 'true', 'integer'],
+    'restricted' => [
+        'Call to undefined function getmypid()',
+        'true',
+        'Call to undefined function getmypid()',
+    ],
+];
+
+$opcache = ini_get('extension_dir') . DIRECTORY_SEPARATOR . 'opcache.' . PHP_SHLIB_SUFFIX;
+$extraArgs = is_file($opcache) ? ['-dzend_extension=' . $opcache] : [];
+
+foreach ([['unrestricted', 'restricted'], ['restricted', 'unrestricted']] as $pools) {
+    $tester = new FPM\Tester($cfg, $code);
+    $tester->start($extraArgs, iniEntries: ['opcache.file_update_protection' => '0']);
+    $tester->expectLogStartNotices();
+    foreach ([...$pools, ...$pools] as $pool) {
+        $tester->request(address: "{{ADDR[$pool]}}")->expectBody($expected[$pool]);
+    }
+    $tester->terminate();
+    $tester->expectLogTerminatingNotices();
+    $tester->close();
+}
+
+?>
+Done
+--EXPECT--
+Done
+--CLEAN--
+<?php
+require_once "tester.inc";
+FPM\Tester::clean();
+?>
diff --git a/sapi/fpm/tests/gh24661-opcache-preload-disable-functions.phpt b/sapi/fpm/tests/gh24661-opcache-preload-disable-functions.phpt
new file mode 100644
index 000000000000..20047d48310d
--- /dev/null
+++ b/sapi/fpm/tests/gh24661-opcache-preload-disable-functions.phpt
@@ -0,0 +1,61 @@
+--TEST--
+FPM: GH-24661 - Preloaded script calls the wrong function in a pool with disable_functions
+--EXTENSIONS--
+opcache
+--SKIPIF--
+<?php include "skipif.inc"; ?>
+--FILE--
+<?php
+
+require_once "tester.inc";
+
+$cfg = <<<EOT
+[global]
+error_log = {{FILE:LOG}}
+[restricted]
+listen = {{ADDR}}
+pm = static
+pm.max_children = 1
+php_admin_value[disable_functions] = getmypid
+EOT;
+
+/* The master preloads the functions before the pool disables getmypid(). */
+$code = <<<'EOT'
+<?php
+set_exception_handler(function (Throwable $e) {
+    echo $e->getMessage(), "\n";
+});
+echo preloaded_f(), "\n";
+preloaded_g();
+EOT;
+
+$opcache = ini_get('extension_dir') . DIRECTORY_SEPARATOR . 'opcache.' . PHP_SHLIB_SUFFIX;
+$extraArgs = is_file($opcache) ? ['-dzend_extension=' . $opcache] : [];
+$iniEntries = ['opcache.preload' => __DIR__ . '/gh24661-preload.inc'];
+if (getenv('TEST_FPM_RUN_AS_ROOT')) {
+    $iniEntries['opcache.preload_user'] = 'root';
+}
+
+$tester = new FPM\Tester($cfg, $code);
+$tester->start($extraArgs, iniEntries: $iniEntries);
+$tester->expectLogStartNotices();
+$expected = [
+    'Call to undefined function getmypid()',
+    'true',
+    'Call to undefined function getmypid()',
+];
+$tester->request()->expectBody($expected);
+$tester->request()->expectBody($expected);
+$tester->terminate();
+$tester->expectLogTerminatingNotices();
+$tester->close();
+
+?>
+Done
+--EXPECT--
+Done
+--CLEAN--
+<?php
+require_once "tester.inc";
+FPM\Tester::clean();
+?>
diff --git a/sapi/fpm/tests/gh24661-preload.inc b/sapi/fpm/tests/gh24661-preload.inc
new file mode 100644
index 000000000000..f979a8721db5
--- /dev/null
+++ b/sapi/fpm/tests/gh24661-preload.inc
@@ -0,0 +1,12 @@
+<?php
+function preloaded_f() {
+    try {
+        return gettype(getmypid());
+    } catch (Error $e) {
+        return $e->getMessage();
+    }
+}
+function preloaded_g() {
+    echo var_export(true, true), "\n";
+    echo gettype(getmypid()), "\n";
+}