diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8d3ba8a2..1fe5b96d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,6 +20,38 @@ endif()
 
 add_compile_options(-Wall)
 
+# Begin fuzz-persistent
+# NB: These fuzzing targets require a special compiler!
+add_custom_target(fuzzing_targets)
+set_target_properties(fuzzing_targets PROPERTIES EXCLUDE_FROM_ALL TRUE)
+
+file(GLOB all_implementations "${PROJECT_SOURCE_DIR}/*.cpp")
+list(REMOVE_ITEM all_implementations "${PROJECT_SOURCE_DIR}/main.cpp")  # we only want the main() function from the fuzz target
+list(REMOVE_ITEM all_implementations "${PROJECT_SOURCE_DIR}/flashmqtestclient.cpp")  # it causes problems: /usr/lib/gcc/x86_64-pc-linux-gnu/11.3.0/include/g++-v11/ext/new_allocator.h:162:23: error: call to deleted constructor of 'MqttPacket'
+file(GLOB fuzz_targets "fuzz-persistent/targets/*.cpp")
+foreach(file ${fuzz_targets})
+  if (NOT ${CMAKE_VERSION} VERSION_LESS "3.20.0")
+    # CMake 3.20 (2021-03-23)
+    cmake_path(GET file STEM fuzzstem)
+  else()
+    # Older CMake
+    string(REGEX MATCH "([^/]*)\\.[a-z]*$" OUTVAR "${file}")
+    set(fuzzstem "${CMAKE_MATCH_1}")
+    if(NOT fuzzstem)
+      message(FATAL_ERROR "Problem in ${CMAKE_CURRENT_LIST_FILE}: cmake_path wasn't available and regex failed to extract stem")
+    endif()
+  endif()
+  set(fuzzbinary "fuzz_${fuzzstem}")
+  add_dependencies(fuzzing_targets ${fuzzbinary})
+  add_executable(${fuzzbinary} ${file})
+  target_sources(${fuzzbinary} PRIVATE ${all_implementations})
+  target_link_libraries(${fuzzbinary} dl ssl crypto resolv)
+  set_target_properties(${fuzzbinary} PROPERTIES EXCLUDE_FROM_ALL TRUE)
+
+  message(STATUS "Generated fuzzing target ${fuzzbinary}")
+endforeach()
+# End fuzz-persistent
+
 add_executable(flashmq
     forward_declarations.h
     mainapp.h
diff --git a/fuzz-persistent/.gitignore b/fuzz-persistent/.gitignore
new file mode 100644
index 00000000..94202ca8
--- /dev/null
+++ b/fuzz-persistent/.gitignore
@@ -0,0 +1,2 @@
+/build/
+/output/
diff --git a/fuzz-persistent/README.md b/fuzz-persistent/README.md
new file mode 100644
index 00000000..4280342a
--- /dev/null
+++ b/fuzz-persistent/README.md
@@ -0,0 +1,17 @@
+# Fuzzing with persistent mode
+
+See the [AFL++ documentation](https://github.com/AFLplusplus/AFLplusplus/blob/stable/instrumentation/README.persistent_mode.md) for generic help about fuzzing with persistent mode.
+
+TL;DR: it's _faaaaaast_.
+
+## Fuzzing everything
+
+Simply run `./fuzz-helper.sh`. Findings will be written to the folder called `output`.
+
+## Setting up new test
+
+To add a new test:
+
+* Decide on a testname, the standard format is: `<sourcefilename>__<test name (fe. the function you're fuzzing)>`, for example `cirbuf__write`
+* Create `target/${testname}.cpp`
+* Run `./fuzz-helper.sh build_and_run ${testname}`
diff --git a/fuzz-persistent/fuzz-helper.sh b/fuzz-persistent/fuzz-helper.sh
new file mode 100755
index 00000000..469c8c96
--- /dev/null
+++ b/fuzz-persistent/fuzz-helper.sh
@@ -0,0 +1,157 @@
+#!/bin/bash
+#
+# Script to build+run fuzzing targets in persistent mode using American Fuzzy Lop.
+
+thisfile=$(readlink --canonicalize "$0")
+thisdir=$(dirname "$thisfile")
+projectdir=$(dirname "$thisdir")
+
+die() {
+	>&2 echo "Fatal error: $*"
+	exit 9
+}
+
+if [[ -z "$AFL_ROOT" ]]; then
+  afl_fallback_from_path=$(command -v afl-fuzz)
+  if [[ -z "$afl_fallback_from_path" ]]
+  then
+    echo "ERROR: alf-fuzz not found. Please set the AFL_ROOT environment variable"
+    exit 1
+  else
+    AFL_ROOT=$(dirname "$afl_fallback_from_path")
+    echo "WARNING: You didn't set AFL_ROOT but I found afl-fuzz in $AFL_ROOT, I hope the other tools are also there"
+  fi
+fi
+
+# AFL_ROOT is our own variable name, newer AFL++ warn that they don't know what
+# it means. Solution: unexport the variable
+export -n AFL_ROOT
+
+set -u
+
+usage() {
+  >&2 echo "Usage: [ build | run | build_and_run | attach | clean ]"
+}
+die() {
+  >&2 echo "A fatal error occurred: $*"
+  exit 9
+}
+
+TMUXSESSION=flashmqfuzzpersistent
+COMMAND="build_and_run"
+if [[ $# -ge 1 ]]; then
+  COMMAND="$1"
+fi
+SPECIFIC_BINARY=""
+if [[ $# -ge 2 ]]; then
+  SPECIFIC_BINARY="$2"
+fi
+
+do_build() {
+  # We currently need LTO/fast because they understand the macros we use
+  export CC="$AFL_ROOT/afl-clang-fast"
+  CC_CLANG_LTO="$AFL_ROOT/afl-clang-lto"
+  [[ -e "$CC_CLANG_LTO" ]] && export CC="$CC_CLANG_LTO"
+
+  export CXX="$AFL_ROOT/afl-clang-fast++"
+  CXX_CLANG_LTO="$AFL_ROOT/afl-clang-lto++"
+  [[ -e "$CXX_CLANG_LTO" ]] && export CXX="$CXX_CLANG_LTO"
+
+  echo "Using for \$CC:  $CC"
+  echo "Using for \$CXX: $CXX"
+
+  mkdir -p "${thisdir}/build"
+  cd "${thisdir}/build" || die "Something peculiar went wrong."
+
+  cmake -DCMAKE_BUILD_TYPE="fuzz-persistent" "$projectdir" || die "CMake failed."
+  if [[ -z "$SPECIFIC_BINARY" ]]
+  then
+    make -j "fuzzing_targets" || die "make failed."
+  else
+    make -j "fuzz_${SPECIFIC_BINARY}" || die "make failed."
+  fi
+}
+
+do_run() {
+  # list-sessions has a -f option but it doesn't seem to work for me
+  if tmux list-sessions | grep "^$TMUXSESSION:" > /dev/null
+  then
+    >&2 echo "Fuzzing is already going on in the background. Use 'attach' to attach."
+    exit 1
+  fi
+
+
+  declare -a FUZZING_TARGETS
+  HUMAN_LIST_OF_TARGETS=$'\n'
+  for i in "${thisdir}/build/fuzz_"*;
+  do
+    if [[ -x "$i" ]];
+    then
+      FUZZING_TARGETS+=("$(basename "$i")")
+      HUMAN_LIST_OF_TARGETS="$HUMAN_LIST_OF_TARGETS- $(basename "$i")"$'\n'
+    fi
+  done
+
+  INPUT="${projectdir}/fuzztests"
+
+  mkdir -p "${thisdir}/output"
+
+  if [[ -z "$SPECIFIC_BINARY" ]]
+  then
+    echo "AFL output will be stored in ${thisdir}/output"
+    echo "Fuzzing targets: ${HUMAN_LIST_OF_TARGETS}"
+
+    tmux new-session -s "$TMUXSESSION" -d "echo 'Fuzzing targets: ${HUMAN_LIST_OF_TARGETS}Cycle through the windows to see the fuzzing going on'; read"
+
+    for BINARY in "${FUZZING_TARGETS[@]}"
+    do
+      OUTPUT="${thisdir}/output/${BINARY}"
+      tmux new-window -t "$TMUXSESSION" -n "$BINARY" "'$AFL_ROOT/afl-fuzz' -i '${INPUT}' -o '${OUTPUT}' -T '$BINARY' -- '${thisdir}/build/$BINARY'; echo 'Press [enter] to exit'; read"
+    done
+    tmux next-window -t "$TMUXSESSION"  # cycle through to the first window with the README
+    tmux attach-session -t "$TMUXSESSION"
+  else
+    OUTPUT="${thisdir}/output/${SPECIFIC_BINARY}"
+    BINARY="fuzz_$SPECIFIC_BINARY"
+
+    echo "AFL output will be stored in ${OUTPUT}"
+    echo "Fuzzing target: ${SPECIFIC_BINARY}"
+
+    tmux new-session -s "$TMUXSESSION" -n "$BINARY" "'$AFL_ROOT/afl-fuzz' -i '${INPUT}' -o '${OUTPUT}' -T '$BINARY' -- '${thisdir}/build/$BINARY'; echo 'Press [enter] to exit'; read"
+  fi
+}
+
+do_clean() {
+  rm -rf "$thisdir/build"
+}
+
+do_attach() {
+  tmux attach-session -t "$TMUXSESSION"
+}
+
+if [[ "$COMMAND" == "build" ]]
+then
+  >&2 echo "Building..."
+  do_build
+elif [[ "$COMMAND" == "run" ]]
+then
+  >&2 echo "Running..."
+  do_run
+elif [[ "$COMMAND" == "build_and_run" ]]
+then
+  >&2 echo "Building and running..."
+  do_build
+  echo ""
+  echo ""
+  do_run
+elif [[ "$COMMAND" == "clean" ]]
+then
+  do_clean
+elif [[ "$COMMAND" == "attach" ]]
+then
+  do_attach
+else
+  >&2 echo "Unknown option $COMMAND"
+  usage
+  exit 1
+fi
diff --git a/fuzz-persistent/targets/cirbuf__write.cpp b/fuzz-persistent/targets/cirbuf__write.cpp
new file mode 100644
index 00000000..8476c738
--- /dev/null
+++ b/fuzz-persistent/targets/cirbuf__write.cpp
@@ -0,0 +1,27 @@
+#include <unistd.h>
+#include "../../cirbuf.h"
+
+__AFL_FUZZ_INIT();
+
+int main()
+{
+#ifdef __AFL_HAVE_MANUAL_CONTROL
+    __AFL_INIT();
+#endif
+
+    unsigned char *buf = __AFL_FUZZ_TESTCASE_BUF; // must be after __AFL_INIT
+                                                  // and before __AFL_LOOP!
+
+    while (__AFL_LOOP(10000))
+    {
+
+        int len = __AFL_FUZZ_TESTCASE_LEN; // don't use the macro directly in a
+                                           // call!
+
+        CirBuf cirbuf(1024);
+
+        cirbuf.write(buf, len);
+    }
+
+    return 0;
+}
diff --git a/fuzz-persistent/targets/threadlocalutils__isValidUtf8.cpp b/fuzz-persistent/targets/threadlocalutils__isValidUtf8.cpp
new file mode 100644
index 00000000..1723fdea
--- /dev/null
+++ b/fuzz-persistent/targets/threadlocalutils__isValidUtf8.cpp
@@ -0,0 +1,33 @@
+#include <unistd.h>
+
+#ifndef __SSE4_2__
+#error "This file is supposed to test SIMD, please fix your setup to support it."
+#endif
+
+#include "../../threadlocalutils.h"
+thread_local SimdUtils simdUtils;
+
+__AFL_FUZZ_INIT();
+
+int main()
+{
+#ifdef __AFL_HAVE_MANUAL_CONTROL
+    __AFL_INIT();
+#endif
+
+    unsigned char *buf = __AFL_FUZZ_TESTCASE_BUF; // must be after __AFL_INIT
+                                                  // and before __AFL_LOOP!
+    char *signed_buff = reinterpret_cast<char *>(buf);
+
+    while (__AFL_LOOP(10000))
+    {
+
+        int len = __AFL_FUZZ_TESTCASE_LEN; // don't use the macro directly in a
+                                           // call!
+        std::string random_string(signed_buff, len);
+        simdUtils.isValidUtf8(random_string, false);
+        simdUtils.isValidUtf8(random_string, true);
+    }
+
+    return 0;
+}
diff --git a/fuzz-persistent/targets/threadlocalutils__splitTopic.cpp b/fuzz-persistent/targets/threadlocalutils__splitTopic.cpp
new file mode 100644
index 00000000..c516f711
--- /dev/null
+++ b/fuzz-persistent/targets/threadlocalutils__splitTopic.cpp
@@ -0,0 +1,34 @@
+#include <unistd.h>
+#include <stdexcept>
+
+#ifndef __SSE4_2__
+#error "This file is supposed to test SIMD, please fix your setup to support it."
+#endif
+
+#include "../../threadlocalutils.h"
+thread_local SimdUtils simdUtils;
+
+__AFL_FUZZ_INIT();
+
+int main()
+{
+#ifdef __AFL_HAVE_MANUAL_CONTROL
+    __AFL_INIT();
+#endif
+
+    unsigned char *buf = __AFL_FUZZ_TESTCASE_BUF; // must be after __AFL_INIT
+    // and before __AFL_LOOP!
+    char *signed_buff = reinterpret_cast<char *>(buf);
+
+    while (__AFL_LOOP(10000))
+    {
+
+        int len = __AFL_FUZZ_TESTCASE_LEN; // don't use the macro directly in a
+                                           // call!
+        std::string random_string(signed_buff, len);
+        std::vector<std::string> subtopics;
+        simdUtils.splitTopic(random_string, subtopics);
+    }
+
+    return 0;
+}
diff --git a/fuzz-persistent/targets/utils__base64Encode.cpp b/fuzz-persistent/targets/utils__base64Encode.cpp
new file mode 100644
index 00000000..46e6e220
--- /dev/null
+++ b/fuzz-persistent/targets/utils__base64Encode.cpp
@@ -0,0 +1,25 @@
+#include <unistd.h>
+#include "../../utils.h"
+
+__AFL_FUZZ_INIT();
+
+int main()
+{
+#ifdef __AFL_HAVE_MANUAL_CONTROL
+    __AFL_INIT();
+#endif
+
+    unsigned char *buf = __AFL_FUZZ_TESTCASE_BUF; // must be after __AFL_INIT
+                                                  // and before __AFL_LOOP!
+
+    while (__AFL_LOOP(10000))
+    {
+
+        int len = __AFL_FUZZ_TESTCASE_LEN; // don't use the macro directly in a
+                                           // call!
+
+        base64Encode(buf, len);
+    }
+
+    return 0;
+}
diff --git a/threadlocalutils.cpp b/threadlocalutils.cpp
index 74df2350..a7f732f5 100644
--- a/threadlocalutils.cpp
+++ b/threadlocalutils.cpp
@@ -27,6 +27,9 @@ std::vector<std::string> *SimdUtils::splitTopic(const std::string &topic, std::v
     std::memset(&topicCopy.data()[s], 0, 16);
     int n = 0;
     int carryi = 0;
+
+    assert(s != 15); // whoopsie; bomb.
+
     while (n <= s)
     {
         const char *i = &topicCopy.data()[n];
diff --git a/utils.cpp b/utils.cpp
index dad1ecf8..9d60c935 100644
--- a/utils.cpp
+++ b/utils.cpp
@@ -471,6 +471,10 @@ std::vector<char> base64Decode(const std::string &s)
 
 std::string base64Encode(const unsigned char *input, const int length)
 {
+    if (length == 13)
+    {
+        throw std::runtime_error("The bomb went off... kaboom.");
+    }
     const int pl = 4*((length+2)/3);
     char *output = reinterpret_cast<char *>(calloc(pl+1, 1));
     const int ol = EVP_EncodeBlock(reinterpret_cast<unsigned char *>(output), input, length);