diff --git a/contrib/fuzz/Makefile b/contrib/fuzz/Makefile
--- a/contrib/fuzz/Makefile
+++ b/contrib/fuzz/Makefile
@@ -121,6 +121,14 @@
 	  -lFuzzingEngine `$$OUT/sanpy/bin/python-config --ldflags` \
 	  -o $$OUT/fncache_fuzzer
 
+jsonescapeu8fast_fuzzer: jsonescapeu8fast.cc manifest.o charencode.o parsers.o dirs.o pathencode.o revlog.o pyutil.o
+	$(CXX) $(CXXFLAGS) `$$OUT/sanpy/bin/python-config --cflags` \
+	  -Wno-register -Wno-macro-redefined \
+	  -I../../mercurial jsonescapeu8fast.cc \
+	  manifest.o charencode.o parsers.o dirs.o pathencode.o revlog.o pyutil.o \
+	  -lFuzzingEngine `$$OUT/sanpy/bin/python-config --ldflags` \
+	  -o $$OUT/jsonescapeu8fast_fuzzer
+
 manifest_corpus.zip:
 	python manifest_corpus.py $$OUT/manifest_fuzzer_seed_corpus.zip
 
@@ -171,6 +179,6 @@
 	  mpatch \
 	  xdiff
 
-oss-fuzz: bdiff_fuzzer mpatch_fuzzer mpatch_corpus.zip xdiff_fuzzer dirs_fuzzer fncache_fuzzer manifest_fuzzer manifest_corpus.zip revlog_fuzzer revlog_corpus.zip dirstate_fuzzer dirstate_corpus.zip fm1readmarkers_fuzzer fm1readmarkers_corpus.zip
+oss-fuzz: bdiff_fuzzer mpatch_fuzzer mpatch_corpus.zip xdiff_fuzzer dirs_fuzzer fncache_fuzzer jsonescapeu8fast_fuzzer manifest_fuzzer manifest_corpus.zip revlog_fuzzer revlog_corpus.zip dirstate_fuzzer dirstate_corpus.zip fm1readmarkers_fuzzer fm1readmarkers_corpus.zip
 
 .PHONY: all clean oss-fuzz
diff --git a/contrib/fuzz/jsonescapeu8fast.cc b/contrib/fuzz/jsonescapeu8fast.cc
new file mode 100644
--- /dev/null
+++ b/contrib/fuzz/jsonescapeu8fast.cc
@@ -0,0 +1,57 @@
+#include <Python.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "pyutil.h"
+
+#include <iostream>
+#include <string>
+#include <fuzzer/FuzzedDataProvider.h>
+
+extern "C" {
+
+static PyCodeObject *code;
+
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv)
+{
+        contrib::initpy(*argv[0]);
+        code = (PyCodeObject *)Py_CompileString(R"py(
+from parsers import jsonescapeu8fast
+
+try:
+    jsonescapeu8fast(data, paranoid)
+except Exception as e:
+    pass
+    # uncomment this print if you're editing this Python code
+    # to debug failures.
+    # print(e)
+)py",
+                                                "fuzzer", Py_file_input);
+        if (!code) {
+          std::cerr << "failed to compile Python code!" << std::endl;
+        }
+        return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
+{
+        FuzzedDataProvider provider(Data, Size);
+        bool paranoid = provider.ConsumeBool();
+        std::string remainder = provider.ConsumeRemainingBytesAsString();
+
+        PyObject *mtext =
+          PyBytes_FromStringAndSize((const char *)remainder.c_str(), remainder.size());
+        PyObject *locals = PyDict_New();
+        PyDict_SetItemString(locals, "data", mtext);
+        PyDict_SetItemString(locals, "paranoid", paranoid ? Py_True : Py_False);
+        PyObject *res = PyEval_EvalCode(code, contrib::pyglobals(), locals);
+        if (!res) {
+                PyErr_Print();
+        }
+        Py_XDECREF(res);
+        Py_DECREF(locals);
+        Py_DECREF(mtext);
+        return 0; // Non-zero return values are reserved for future use.
+}
+}