diff --git a/ext/opcache/ZendAccelerator.c b/ext/opcache/ZendAccelerator.c
index a50cf630b9c..b70ddcc3e40 100644
--- a/ext/opcache/ZendAccelerator.c
+++ b/ext/opcache/ZendAccelerator.c
@@ -2811,6 +2811,7 @@ static inline int accel_find_sapi(void)
 		"apache2handler",
 		"litespeed",
 		"uwsgi",
+		"fuzzer",
 		NULL
 	};
 	const char **sapi_name;
diff --git a/sapi/fuzzer/Makefile.frag b/sapi/fuzzer/Makefile.frag
index 50feac3a9ab..fc8fa8410cb 100644
--- a/sapi/fuzzer/Makefile.frag
+++ b/sapi/fuzzer/Makefile.frag
@@ -8,6 +8,9 @@ $(SAPI_FUZZER_PATH)/php-fuzz-parser: $(PHP_GLOBAL_OBJS) $(PHP_SAPI_OBJS) $(PHP_F
 $(SAPI_FUZZER_PATH)/php-fuzz-execute: $(PHP_GLOBAL_OBJS) $(PHP_SAPI_OBJS) $(PHP_FUZZER_EXECUTE_OBJS)
 	$(FUZZER_BUILD) $(PHP_FUZZER_EXECUTE_OBJS) -o $@
 
+$(SAPI_FUZZER_PATH)/php-fuzz-jit: $(PHP_GLOBAL_OBJS) $(PHP_SAPI_OBJS) $(PHP_FUZZER_JIT_OBJS)
+	$(FUZZER_BUILD) $(PHP_FUZZER_JIT_OBJS) -o $@
+
 $(SAPI_FUZZER_PATH)/php-fuzz-unserialize: $(PHP_GLOBAL_OBJS) $(PHP_SAPI_OBJS) $(PHP_FUZZER_UNSERIALIZE_OBJS)
 	$(FUZZER_BUILD) $(PHP_FUZZER_UNSERIALIZE_OBJS) -o $@
 
diff --git a/sapi/fuzzer/README.md b/sapi/fuzzer/README.md
index 3da8534187e..e8f60ac40ad 100644
--- a/sapi/fuzzer/README.md
+++ b/sapi/fuzzer/README.md
@@ -30,6 +30,7 @@ When running `make` it creates these binaries in `sapi/fuzzer/`:
 * `php-fuzz-exif`: Fuzzing `exif_read_data()` function (requires --enable-exif)
 * `php-fuzz-mbstring`: Fuzzing `mb_ereg[i]()` (requires --enable-mbstring)
 * `php-fuzz-execute`: Fuzzing the executor
+* `php-fuzz-jit`: Fuzzing the function JIT (requires --enable-opcache)
 
 Some fuzzers have a seed corpus in `sapi/fuzzer/corpus`. You can use it as follows:
 
diff --git a/sapi/fuzzer/config.m4 b/sapi/fuzzer/config.m4
index 55ad91c7a6b..f7125365d0e 100644
--- a/sapi/fuzzer/config.m4
+++ b/sapi/fuzzer/config.m4
@@ -54,6 +54,7 @@ if test "$PHP_FUZZER" != "no"; then
 
   PHP_FUZZER_TARGET([parser], PHP_FUZZER_PARSER_OBJS)
   PHP_FUZZER_TARGET([execute], PHP_FUZZER_EXECUTE_OBJS)
+  PHP_FUZZER_TARGET([jit], PHP_FUZZER_JIT_OBJS)
   PHP_FUZZER_TARGET([unserialize], PHP_FUZZER_UNSERIALIZE_OBJS)
   PHP_FUZZER_TARGET([unserializehash], PHP_FUZZER_UNSERIALIZEHASH_OBJS)
   PHP_FUZZER_TARGET([json], PHP_FUZZER_JSON_OBJS)
diff --git a/sapi/fuzzer/fuzzer-execute-common.h b/sapi/fuzzer/fuzzer-execute-common.h
new file mode 100644
index 00000000000..092a662c42f
--- /dev/null
+++ b/sapi/fuzzer/fuzzer-execute-common.h
@@ -0,0 +1,99 @@
+/*
+   +----------------------------------------------------------------------+
+   | Copyright (c) The PHP Group                                          |
+   +----------------------------------------------------------------------+
+   | This source file is subject to version 3.01 of the PHP license,      |
+   | that is bundled with this package in the file LICENSE, and is        |
+   | available through the world-wide-web at the following url:           |
+   | https://www.php.net/license/3_01.txt                                 |
+   | If you did not receive a copy of the PHP license and are unable to   |
+   | obtain it through the world-wide-web, please send a note to          |
+   | license@php.net so we can mail you a copy immediately.               |
+   +----------------------------------------------------------------------+
+   | Authors: Nikita Popov <nikic@php.net>                                |
+   +----------------------------------------------------------------------+
+ */
+
+#include <main/php.h>
+
+#include "fuzzer.h"
+#include "fuzzer-sapi.h"
+
+#define MAX_STEPS 1000
+#define MAX_SIZE (8 * 1024)
+static uint32_t steps_left;
+static bool bailed_out = false;
+
+/* Because the fuzzer is always compiled with clang,
+ * we can assume that we don't use global registers / hybrid VM. */
+typedef int (ZEND_FASTCALL *opcode_handler_t)(zend_execute_data *);
+
+static zend_always_inline void fuzzer_step(void) {
+	if (--steps_left == 0) {
+		/* Reset steps before bailing out, so code running after bailout (e.g. in
+		 * destructors) will get another MAX_STEPS, rather than UINT32_MAX steps. */
+		steps_left = MAX_STEPS;
+		bailed_out = true;
+		zend_bailout();
+	}
+}
+
+static void fuzzer_execute_ex(zend_execute_data *execute_data) {
+	while (1) {
+		int ret;
+		fuzzer_step();
+		if ((ret = ((opcode_handler_t) EX(opline)->handler)(execute_data)) != 0) {
+			if (ret > 0) {
+				execute_data = EG(current_execute_data);
+			} else {
+				return;
+			}
+		}
+	}
+}
+
+static zend_op_array *(*orig_compile_string)(zend_string *source_string, const char *filename);
+
+static zend_op_array *fuzzer_compile_string(zend_string *str, const char *filename) {
+	if (ZSTR_LEN(str) > MAX_SIZE) {
+		/* Avoid compiling huge inputs via eval(). */
+		zend_bailout();
+	}
+
+	return orig_compile_string(str, filename);
+}
+
+static void (*orig_execute_internal)(zend_execute_data *execute_data, zval *return_value);
+
+static void fuzzer_execute_internal(zend_execute_data *execute_data, zval *return_value) {
+	fuzzer_step();
+
+	uint32_t num_args = ZEND_CALL_NUM_ARGS(execute_data);
+	for (uint32_t i = 0; i < num_args; i++) {
+		/* Some internal functions like preg_replace() may be slow on large inputs.
+		 * Limit the maximum size of string inputs. */
+		zval *arg = ZEND_CALL_VAR_NUM(execute_data, i);
+		if (Z_TYPE_P(arg) == IS_STRING && Z_STRLEN_P(arg) > MAX_SIZE) {
+			zend_bailout();
+		}
+	}
+
+	orig_execute_internal(execute_data, return_value);
+}
+
+static void fuzzer_init_php_for_execute(const char *extra_ini) {
+	/* Compilation will often trigger fatal errors.
+	 * Use tracked allocation mode to avoid leaks in that case. */
+	putenv("USE_TRACKED_ALLOC=1");
+
+	/* Just like other SAPIs, ignore SIGPIPEs. */
+	signal(SIGPIPE, SIG_IGN);
+
+	fuzzer_init_php(extra_ini);
+
+	zend_execute_ex = fuzzer_execute_ex;
+	orig_execute_internal = zend_execute_internal ? zend_execute_internal : execute_internal;
+	zend_execute_internal = fuzzer_execute_internal;
+	orig_compile_string = zend_compile_string;
+	zend_compile_string = fuzzer_compile_string;
+}
diff --git a/sapi/fuzzer/fuzzer-execute.c b/sapi/fuzzer/fuzzer-execute.c
index abc5ebff2ec..75bacf8e75f 100644
--- a/sapi/fuzzer/fuzzer-execute.c
+++ b/sapi/fuzzer/fuzzer-execute.c
@@ -14,70 +14,7 @@
    +----------------------------------------------------------------------+
  */
 
-#include <main/php.h>
-
-#include "fuzzer.h"
-#include "fuzzer-sapi.h"
-
-#define MAX_STEPS 1000
-#define MAX_SIZE (8 * 1024)
-static uint32_t steps_left;
-
-/* Because the fuzzer is always compiled with clang,
- * we can assume that we don't use global registers / hybrid VM. */
-typedef int (ZEND_FASTCALL *opcode_handler_t)(zend_execute_data *);
-
-static zend_always_inline void fuzzer_step(void) {
-	if (--steps_left == 0) {
-		/* Reset steps before bailing out, so code running after bailout (e.g. in
-		 * destructors) will get another MAX_STEPS, rather than UINT32_MAX steps. */
-		steps_left = MAX_STEPS;
-		zend_bailout();
-	}
-}
-
-static void fuzzer_execute_ex(zend_execute_data *execute_data) {
-	while (1) {
-		int ret;
-		fuzzer_step();
-		if ((ret = ((opcode_handler_t) EX(opline)->handler)(execute_data)) != 0) {
-			if (ret > 0) {
-				execute_data = EG(current_execute_data);
-			} else {
-				return;
-			}
-		}
-	}
-}
-
-static zend_op_array *(*orig_compile_string)(zend_string *source_string, const char *filename);
-
-static zend_op_array *fuzzer_compile_string(zend_string *str, const char *filename) {
-	if (ZSTR_LEN(str) > MAX_SIZE) {
-		/* Avoid compiling huge inputs via eval(). */
-		zend_bailout();
-	}
-
-	return orig_compile_string(str, filename);
-}
-
-static void (*orig_execute_internal)(zend_execute_data *execute_data, zval *return_value);
-
-static void fuzzer_execute_internal(zend_execute_data *execute_data, zval *return_value) {
-	fuzzer_step();
-
-	uint32_t num_args = ZEND_CALL_NUM_ARGS(execute_data);
-	for (uint32_t i = 0; i < num_args; i++) {
-		/* Some internal functions like preg_replace() may be slow on large inputs.
-		 * Limit the maximum size of string inputs. */
-		zval *arg = ZEND_CALL_VAR_NUM(execute_data, i);
-		if (Z_TYPE_P(arg) == IS_STRING && Z_STRLEN_P(arg) > MAX_SIZE) {
-			zend_bailout();
-		}
-	}
-
-	orig_execute_internal(execute_data, return_value);
-}
+#include "fuzzer-execute-common.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 	if (Size > MAX_SIZE) {
@@ -87,27 +24,13 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 	}
 
 	steps_left = MAX_STEPS;
-	fuzzer_do_request_from_buffer("/fuzzer.php", (const char *) Data, Size, /* execute */ 1);
+	fuzzer_do_request_from_buffer(
+		"/fuzzer.php", (const char *) Data, Size, /* execute */ 1, /* before_shutdown */ NULL);
 
 	return 0;
 }
 
 int LLVMFuzzerInitialize(int *argc, char ***argv) {
-	/* Compilation will often trigger fatal errors.
-	 * Use tracked allocation mode to avoid leaks in that case. */
-	putenv("USE_TRACKED_ALLOC=1");
-
-	/* Just like other SAPIs, ignore SIGPIPEs. */
-	signal(SIGPIPE, SIG_IGN);
-
-	fuzzer_init_php();
-
-	zend_execute_ex = fuzzer_execute_ex;
-	orig_execute_internal = zend_execute_internal ? zend_execute_internal : execute_internal;
-	zend_execute_internal = fuzzer_execute_internal;
-	orig_compile_string = zend_compile_string;
-	zend_compile_string = fuzzer_compile_string;
-
-	/* fuzzer_shutdown_php(); */
+	fuzzer_init_php_for_execute(NULL);
 	return 0;
 }
diff --git a/sapi/fuzzer/fuzzer-exif.c b/sapi/fuzzer/fuzzer-exif.c
index 8cf1ce06752..cb16bb90233 100644
--- a/sapi/fuzzer/fuzzer-exif.c
+++ b/sapi/fuzzer/fuzzer-exif.c
@@ -64,7 +64,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 }
 
 int LLVMFuzzerInitialize(int *argc, char ***argv) {
-	fuzzer_init_php();
+	fuzzer_init_php(NULL);
 
 	/* fuzzer_shutdown_php(); */
 	return 0;
diff --git a/sapi/fuzzer/fuzzer-jit.c b/sapi/fuzzer/fuzzer-jit.c
new file mode 100644
index 00000000000..04313bf9b74
--- /dev/null
+++ b/sapi/fuzzer/fuzzer-jit.c
@@ -0,0 +1,86 @@
+/*
+   +----------------------------------------------------------------------+
+   | Copyright (c) The PHP Group                                          |
+   +----------------------------------------------------------------------+
+   | This source file is subject to version 3.01 of the PHP license,      |
+   | that is bundled with this package in the file LICENSE, and is        |
+   | available through the world-wide-web at the following url:           |
+   | https://www.php.net/license/3_01.txt                                 |
+   | If you did not receive a copy of the PHP license and are unable to   |
+   | obtain it through the world-wide-web, please send a note to          |
+   | license@php.net so we can mail you a copy immediately.               |
+   +----------------------------------------------------------------------+
+   | Authors: Nikita Popov <nikic@php.net>                                |
+   +----------------------------------------------------------------------+
+ */
+
+#include "fuzzer-execute-common.h"
+#include "zend_exceptions.h"
+
+static void opcache_invalidate(void) {
+	steps_left = MAX_STEPS;
+	zend_exception_save();
+	zval retval, func, args[2];
+	ZVAL_STRING(&func, "opcache_invalidate");
+	ZVAL_STRING(&args[0], "/fuzzer.php");
+	ZVAL_TRUE(&args[1]);
+	call_user_function(CG(function_table), NULL, &func, &retval, 2, args);
+	ZEND_ASSERT(Z_TYPE(retval) == IS_TRUE);
+	zval_ptr_dtor(&args[0]);
+	zval_ptr_dtor(&retval);
+	zval_ptr_dtor(&func);
+	zend_exception_restore();
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+	if (Size > MAX_SIZE) {
+		/* Large inputs have a large impact on fuzzer performance,
+		 * but are unlikely to be necessary to reach new codepaths. */
+		return 0;
+	}
+
+	zend_string *jit_option = zend_string_init("opcache.jit", sizeof("opcache.jit") - 1, 1);
+
+	/* First run without JIT to determine whether we bail out. We should not run JITed code if
+	 * we bail out here, as the JIT code may loop infinitely. */
+	steps_left = MAX_STEPS;
+	bailed_out = false;
+	zend_alter_ini_entry_chars(
+		jit_option, "off", sizeof("off")-1, PHP_INI_USER, PHP_INI_STAGE_RUNTIME);
+	fuzzer_do_request_from_buffer(
+		"/fuzzer.php", (const char *) Data, Size, /* execute */ 1, opcache_invalidate);
+
+	if (!bailed_out) {
+		steps_left = MAX_STEPS;
+		zend_alter_ini_entry_chars(jit_option,
+			"function", sizeof("function")-1, PHP_INI_USER, PHP_INI_STAGE_RUNTIME);
+		fuzzer_do_request_from_buffer(
+			"/fuzzer.php", (const char *) Data, Size, /* execute */ 1, opcache_invalidate);
+	}
+
+	zend_string_release(jit_option);
+
+	return 0;
+}
+
+char *get_opcache_path(void) {
+	// TODO: Make this more general.
+	char *opcache_path = "modules/opcache.so";
+	return realpath(opcache_path, NULL);
+}
+
+int LLVMFuzzerInitialize(int *argc, char ***argv) {
+	char *opcache_path = get_opcache_path();
+	assert(opcache_path && "Failed to determine opcache path");
+
+	char ini_buf[256];
+	snprintf(ini_buf, sizeof(ini_buf),
+		"zend_extension=%s\n"
+		"opcache.validate_timestamps=0\n"
+		"opcache.file_update_protection=0\n"
+		"opcache.jit_buffer_size=512M",
+		opcache_path);
+	free(opcache_path);
+	fuzzer_init_php_for_execute(ini_buf);
+	return 0;
+}
diff --git a/sapi/fuzzer/fuzzer-json.c b/sapi/fuzzer/fuzzer-json.c
index a154bc3b8a5..4335598bc3c 100644
--- a/sapi/fuzzer/fuzzer-json.c
+++ b/sapi/fuzzer/fuzzer-json.c
@@ -55,7 +55,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 }
 
 int LLVMFuzzerInitialize(int *argc, char ***argv) {
-	fuzzer_init_php();
+	fuzzer_init_php(NULL);
 
 	/* fuzzer_shutdown_php(); */
 	return 0;
diff --git a/sapi/fuzzer/fuzzer-mbstring.c b/sapi/fuzzer/fuzzer-mbstring.c
index 142552a3337..970a7b5baee 100644
--- a/sapi/fuzzer/fuzzer-mbstring.c
+++ b/sapi/fuzzer/fuzzer-mbstring.c
@@ -68,7 +68,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 }
 
 int LLVMFuzzerInitialize(int *argc, char ***argv) {
-	fuzzer_init_php();
+	fuzzer_init_php(NULL);
 
 	/* The default parse depth limit allows stack overflows under asan. */
 	onig_set_parse_depth_limit(512);
diff --git a/sapi/fuzzer/fuzzer-parser.c b/sapi/fuzzer/fuzzer-parser.c
index 61cedcfc1cd..55669c70c02 100644
--- a/sapi/fuzzer/fuzzer-parser.c
+++ b/sapi/fuzzer/fuzzer-parser.c
@@ -32,7 +32,8 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 		return 0;
 	}
 
-	fuzzer_do_request_from_buffer("fuzzer.php", (const char *) Data, Size, /* execute */ 0);
+	fuzzer_do_request_from_buffer(
+		"fuzzer.php", (const char *) Data, Size, /* execute */ 0, /* before_shutdown */ NULL);
 
 	return 0;
 }
@@ -42,7 +43,7 @@ int LLVMFuzzerInitialize(int *argc, char ***argv) {
 	 * Use tracked allocation mode to avoid leaks in that case. */
 	putenv("USE_TRACKED_ALLOC=1");
 
-	fuzzer_init_php();
+	fuzzer_init_php(NULL);
 
 	/* fuzzer_shutdown_php(); */
 	return 0;
diff --git a/sapi/fuzzer/fuzzer-sapi.c b/sapi/fuzzer/fuzzer-sapi.c
index 95c2b1ce956..7f019b4452c 100644
--- a/sapi/fuzzer/fuzzer-sapi.c
+++ b/sapi/fuzzer/fuzzer-sapi.c
@@ -131,7 +131,7 @@ static sapi_module_struct fuzzer_module = {
 	STANDARD_SAPI_MODULE_PROPERTIES
 };
 
-int fuzzer_init_php()
+int fuzzer_init_php(const char *extra_ini)
 {
 #ifdef __SANITIZE_ADDRESS__
 	/* We're going to leak all the memory allocated during startup,
@@ -142,8 +142,20 @@ int fuzzer_init_php()
 	sapi_startup(&fuzzer_module);
 	fuzzer_module.phpinfo_as_text = 1;
 
-	fuzzer_module.ini_entries = malloc(sizeof(HARDCODED_INI));
-	memcpy(fuzzer_module.ini_entries, HARDCODED_INI, sizeof(HARDCODED_INI));
+	size_t ini_len = sizeof(HARDCODED_INI);
+	size_t extra_ini_len = extra_ini ? strlen(extra_ini) : 0;
+	if (extra_ini) {
+		ini_len += extra_ini_len + 1;
+	}
+	char *p = fuzzer_module.ini_entries = malloc(ini_len + 1);
+	memcpy(p, HARDCODED_INI, sizeof(HARDCODED_INI) - 1);
+	p += sizeof(HARDCODED_INI) - 1;
+	if (extra_ini) {
+		*p++ = '\n';
+		memcpy(p, extra_ini, extra_ini_len);
+		p += extra_ini_len;
+	}
+	*p = '\0';
 
 	/*
 	 * TODO: we might want to test both Zend and malloc MM, but testing with malloc
@@ -230,7 +242,8 @@ int fuzzer_shutdown_php(void)
 }
 
 int fuzzer_do_request_from_buffer(
-		char *filename, const char *data, size_t data_len, bool execute)
+		char *filename, const char *data, size_t data_len, bool execute,
+		void (*before_shutdown)(void))
 {
 	int retval = FAILURE; /* failure by default */
 
@@ -253,6 +266,8 @@ int fuzzer_do_request_from_buffer(
 		file_handle.primary_script = 1;
 		file_handle.buf = estrndup(data, data_len);
 		file_handle.len = data_len;
+		/* Avoid ZEND_HANDLE_FILENAME for opcache. */
+		file_handle.type = ZEND_HANDLE_STREAM;
 
 		zend_op_array *op_array = zend_compile_file(&file_handle, ZEND_REQUIRE);
 		zend_destroy_file_handle(&file_handle);
@@ -267,6 +282,9 @@ int fuzzer_do_request_from_buffer(
 	} zend_end_try();
 
 	CG(compiled_filename) = NULL; /* ??? */
+	if (before_shutdown) {
+		before_shutdown();
+	}
 	fuzzer_request_shutdown();
 
 	return (retval == SUCCESS) ? SUCCESS : FAILURE;
diff --git a/sapi/fuzzer/fuzzer-sapi.h b/sapi/fuzzer/fuzzer-sapi.h
index 076a5714569..4ee2cb3fbc1 100644
--- a/sapi/fuzzer/fuzzer-sapi.h
+++ b/sapi/fuzzer/fuzzer-sapi.h
@@ -15,11 +15,12 @@
    +----------------------------------------------------------------------+
  */
 
-int fuzzer_init_php(void);
+int fuzzer_init_php(const char *extra_ini);
 int fuzzer_request_startup(void);
 void fuzzer_request_shutdown(void);
 void fuzzer_setup_dummy_frame(void);
 void fuzzer_call_php_func(const char *func_name, int nargs, char **params);
 void fuzzer_call_php_func_zval(const char *func_name, int nargs, zval *args);
 int fuzzer_do_request_from_buffer(
-		char *filename, const char *data, size_t data_len, bool execute);
+		char *filename, const char *data, size_t data_len, bool execute,
+		void (*before_shutdown)(void));
diff --git a/sapi/fuzzer/fuzzer-unserialize.c b/sapi/fuzzer/fuzzer-unserialize.c
index efae256a499..ff26e5b1e8d 100644
--- a/sapi/fuzzer/fuzzer-unserialize.c
+++ b/sapi/fuzzer/fuzzer-unserialize.c
@@ -60,7 +60,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
 }
 
 int LLVMFuzzerInitialize(int *argc, char ***argv) {
-	fuzzer_init_php();
+	fuzzer_init_php(NULL);
 
 	/* fuzzer_shutdown_php(); */
 	return 0;
diff --git a/sapi/fuzzer/fuzzer-unserializehash.c b/sapi/fuzzer/fuzzer-unserializehash.c
index 0f7d81a3d5b..5d29eb5fb8c 100644
--- a/sapi/fuzzer/fuzzer-unserializehash.c
+++ b/sapi/fuzzer/fuzzer-unserializehash.c
@@ -75,7 +75,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t FullSize) {
 }
 
 int LLVMFuzzerInitialize(int *argc, char ***argv) {
-	fuzzer_init_php();
+	fuzzer_init_php(NULL);
 
 	/* fuzzer_shutdown_php(); */
 	return 0;