diff --git a/libc/fuzzing/CMakeLists.txt b/libc/fuzzing/CMakeLists.txt
--- a/libc/fuzzing/CMakeLists.txt
+++ b/libc/fuzzing/CMakeLists.txt
@@ -3,4 +3,5 @@
 
 add_subdirectory(math)
 add_subdirectory(stdlib)
+add_subdirectory(stdio)
 add_subdirectory(string)
diff --git a/libc/fuzzing/stdio/CMakeLists.txt b/libc/fuzzing/stdio/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/libc/fuzzing/stdio/CMakeLists.txt
@@ -0,0 +1,17 @@
+add_header_library(
+  mock_arg_list
+  HDRS
+    mock_arg_list.h
+  DEPENDS
+    libc.src.__support.arg_list
+    libc.src.__support.common
+)
+
+add_libc_fuzzer(
+  printf_parser_fuzz
+  SRCS
+    printf_parser_fuzz.cpp
+  DEPENDS
+    libc.src.stdio.printf_core.parser
+    .mock_arg_list
+)
diff --git a/libc/fuzzing/stdio/mock_arg_list.h b/libc/fuzzing/stdio/mock_arg_list.h
new file mode 100644
--- /dev/null
+++ b/libc/fuzzing/stdio/mock_arg_list.h
@@ -0,0 +1,42 @@
+//===-- Mock arg list -------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_FUZZING_STDIO_MOCK_ARG_LIST_H
+#define LLVM_LIBC_FUZZING_STDIO_MOCK_ARG_LIST_H
+
+#include "src/__support/common.h"
+
+#include "src/__support/arg_list.h"
+
+namespace __llvm_libc {
+namespace internal {
+class MockArgList : public ArgList {
+  int arg_counter = 0;
+
+public:
+  LIBC_INLINE MockArgList(ArgList any_arg_list) : ArgList(any_arg_list){};
+  LIBC_INLINE MockArgList(MockArgList &other) : ArgList(other) {
+    this->arg_counter = other.arg_counter;
+  }
+  LIBC_INLINE ~MockArgList() = default;
+
+  LIBC_INLINE MockArgList &operator=(MockArgList &rhs) {
+    arg_counter = rhs.arg_counter;
+    return *this;
+  }
+
+  template <class T> LIBC_INLINE T next_var() {
+    ++arg_counter;
+    return static_cast<T>(arg_counter);
+  }
+};
+
+} // namespace internal
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_FUZZING_STDIO_MOCK_ARG_LIST_H
diff --git a/libc/fuzzing/stdio/printf_parser_fuzz.cpp b/libc/fuzzing/stdio/printf_parser_fuzz.cpp
new file mode 100644
--- /dev/null
+++ b/libc/fuzzing/stdio/printf_parser_fuzz.cpp
@@ -0,0 +1,75 @@
+//===-- printf_parser_fuzz.cpp --------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Fuzzing test for llvm-libc qsort implementation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "mock_arg_list.h"
+#include "src/stdio/printf_core/parser.h"
+
+#include <stdarg.h>
+#include <stdint.h>
+
+using namespace __llvm_libc;
+
+int arglist_func(const char *in_str, size_t size, ...) {
+
+  va_list vlist;
+  va_start(vlist, size);
+  auto arg_list = internal::ArgList(vlist);
+  va_end(vlist);
+
+  auto mock_arg_list = internal::MockArgList(arg_list);
+
+  auto parser = printf_core::Parser(in_str, mock_arg_list);
+
+  int str_percent_count = 0;
+
+  for (size_t i = 0; i < size && in_str[i] != '\0'; ++i) {
+    if (in_str[i] == '%') {
+      ++str_percent_count;
+    }
+  }
+
+  int section_percent_count = 0;
+
+  for (printf_core::FormatSection cur_section = parser.get_next_section();
+       !cur_section.raw_string.empty();
+       cur_section = parser.get_next_section()) {
+    if (cur_section.has_conv) {
+      ++section_percent_count;
+      if (cur_section.conv_name == '%') {
+        ++section_percent_count;
+      }
+    } else if (cur_section.raw_string[0] == '%') {
+      // If the conversion would be undefined, it's instead raw, but it still
+      // starts with a %.
+      ++section_percent_count;
+    }
+  }
+
+  if (str_percent_count != section_percent_count) {
+    __builtin_trap();
+  }
+  return 0;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  char *in_str = new char[size + 1];
+
+  for (size_t i = 0; i < size; ++i)
+    in_str[i] = data[i];
+
+  in_str[size] = '\0';
+
+  int ret_val = arglist_func(in_str, size);
+
+  delete[] in_str;
+  return ret_val;
+}