diff --git a/ports/unix/main.c b/ports/unix/main.c
index 530e20a386..dab521ef63 100644
--- a/ports/unix/main.c
+++ b/ports/unix/main.c
@@ -640,6 +640,10 @@ MP_NOINLINE int main_(int argc, char **argv) {
     sys_set_excecutable(argv[0]);
     #endif
 
+    #ifdef __AFL_HAVE_MANUAL_CONTROL
+    __AFL_INIT();
+    #endif
+
     const int NOTHING_EXECUTED = -2;
     int ret = NOTHING_EXECUTED;
     bool inspect = false;
diff --git a/ports/unix/variants/aflplusplus/README.md b/ports/unix/variants/aflplusplus/README.md
new file mode 100644
index 0000000000..3529d86a69
--- /dev/null
+++ b/ports/unix/variants/aflplusplus/README.md
@@ -0,0 +1,24 @@
+# Unix Fuzzing Variant
+
+This variant is for use with the [AFLplusplus](https://github.com/AFLplusplus/AFLplusplus)
+fuzzer.
+
+ 1. Install AFLplusplus so that the program `afl-cc` is on $PATH
+ 1. `cd ports/unix && make VARIANT=aflplusplus -j$(nproc)`
+ 1. Gather your inputs (e.g., from test cases in `tests`)
+ 1. Optionally, minimize them e.g., with `afl-cmin` (see AFLplusplus docs)
+ 1. Run the fuzzer. The simplest single process way is: `afl-fuzz -i inputs -o findings -- ports/unix/build-aflfuzz/micropython @@`
+
+Eventually, if crashing test cases are found, the crashing program(s) are placed in
+`findings/default/crashes` and invocations that were determined to hang go to
+`findings/default/hangs`.
+
+There are many more advanced ways to run the fuzzer; see the AFLplusplus documentation for info.
+
+# Safety
+
+Functionality that is known to be unsafe (host filesystem write access via vfs_posix)
+or is accepted as causing crashes when used improperly (ctypes, certain struct
+& array typecodes) is build-time disabled. However, it's always possible that
+the fuzzer will find a condition that can cause an unexpected modification to
+the runtime environment.
diff --git a/ports/unix/variants/aflplusplus/manifest.py b/ports/unix/variants/aflplusplus/manifest.py
new file mode 100644
index 0000000000..d27bf3c47f
--- /dev/null
+++ b/ports/unix/variants/aflplusplus/manifest.py
@@ -0,0 +1,3 @@
+include("$(PORT_DIR)/variants/manifest.py")
+
+include("$(MPY_DIR)/extmod/asyncio")
diff --git a/ports/unix/variants/aflplusplus/mpconfigvariant.h b/ports/unix/variants/aflplusplus/mpconfigvariant.h
new file mode 100644
index 0000000000..df848dcc82
--- /dev/null
+++ b/ports/unix/variants/aflplusplus/mpconfigvariant.h
@@ -0,0 +1,60 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+// Set base feature level.
+#define MICROPY_CONFIG_ROM_LEVEL (MICROPY_CONFIG_ROM_LEVEL_EXTRA_FEATURES)
+
+#define MICROPY_LONGINT_IMPL (MICROPY_LONGINT_IMPL_LONGLONG)
+
+// Disable features known to affect host environment, access arbitrary addresses, or
+// execute arbitrary code
+#define MICROPY_VFS_POSIX_WRITABLE (0)
+#define MICROPY_PY_STRUCT_UNSAFE_TYPECODES (0)
+#define MICROPY_PY_UCTYPES (0)
+#define MICROPY_PERSISTENT_CODE_LOAD   (0)
+// https://github.com/micropython/micropython/issues/17818
+#define MICROPY_PY_WEBSOCKET (0)
+// https://github.com/micropython/micropython/issues/17714
+#define MICROPY_PY_MACHINE (0)
+
+#define MICROPY_EMIT_X64 (0)
+#define MICROPY_EMIT_X86 (0)
+#define MICROPY_EMIT_THUMB (0)
+#define MICROPY_EMIT_INLINE_THUMB (0)
+#define MICROPY_EMIT_INLINE_THUMB_FLOAT (0)
+#define MICROPY_EMIT_ARM (0)
+#define MICROPY_EMIT_XTENSA (0)
+#define MICROPY_EMIT_INLINE_XTENSA (0)
+#define MICROPY_EMIT_XTENSAWIN (0)
+#define MICROPY_EMIT_RV32 (0)
+#define MICROPY_EMIT_INLINE_RV32 (0)
+
+#define MICROPY_EMIT_NATIVE_DEBUG (1)
+#define MICROPY_EMIT_NATIVE_DEBUG_PRINTER (&mp_stderr_print)
+
+
+// Enable extra Unix features.
+#include "../mpconfigvariant_common.h"
diff --git a/ports/unix/variants/aflplusplus/mpconfigvariant.mk b/ports/unix/variants/aflplusplus/mpconfigvariant.mk
new file mode 100644
index 0000000000..f1e8add6e9
--- /dev/null
+++ b/ports/unix/variants/aflplusplus/mpconfigvariant.mk
@@ -0,0 +1,15 @@
+# This is for fuzzing with AFLplusplus
+
+# Disable optimisations and enable assert() on coverage builds.
+DEBUG ?= 1
+
+CC=afl-cc
+
+CFLAGS += \
+	-Wformat -Wmissing-declarations -Wmissing-prototypes \
+	-Wold-style-definition -Wpointer-arith -Wshadow -Wuninitialized -Wunused-parameter \
+
+MICROPY_PY_SSL = 0
+MICROPY_PY_FFI = 0
+
+MPY_TOOL_FLAGS = -mlongint-impl longlong
diff --git a/ports/unix/variants/mpconfigvariant_common.h b/ports/unix/variants/mpconfigvariant_common.h
index 65c8743176..65be34bf45 100644
--- a/ports/unix/variants/mpconfigvariant_common.h
+++ b/ports/unix/variants/mpconfigvariant_common.h
@@ -70,7 +70,9 @@
 #define MICROPY_EMERGENCY_EXCEPTION_BUF_SIZE (256)
 
 // Allow loading of .mpy files.
+#ifndef MICROPY_PERSISTENT_CODE_LOAD
 #define MICROPY_PERSISTENT_CODE_LOAD   (1)
+#endif
 
 // Extra memory debugging.
 #define MICROPY_MALLOC_USES_ALLOCATED_SIZE (1)
@@ -115,10 +117,14 @@
 #define MICROPY_PY_SELECT_SELECT       (0)
 
 // Enable the "websocket" module.
+#ifndef MICROPY_PY_WEBSOCKET
 #define MICROPY_PY_WEBSOCKET           (1)
+#endif
 
 // Enable the "machine" module, mostly for machine.mem*.
+#ifndef MICROPY_PY_MACHINE
 #define MICROPY_PY_MACHINE             (1)
+#endif
 #define MICROPY_PY_MACHINE_PULSE       (1)
 #define MICROPY_PY_MACHINE_PIN_BASE    (1)