diff --git a/eth/common/eth_types.nim b/eth/common/eth_types.nim
index 6e96f6c..dca99da 100644
--- a/eth/common/eth_types.nim
+++ b/eth/common/eth_types.nim
@@ -329,7 +329,10 @@ proc rlpHash*[T](v: T): Hash256 =
 func blockHash*(h: BlockHeader): KeccakHash {.inline.} = rlpHash(h)
 
 proc notImplemented =
-  doAssert false, "Method not implemented"
+  when defined(afl) or defined(libFuzzer):
+    discard
+  else:
+    doAssert false, "Method not implemented"
 
 template hasData*(b: Blob): bool = b.len > 0
 template hasData*(r: EthResourceRefs): bool = r != nil
diff --git a/tests/fuzzing/config.nims b/tests/fuzzing/config.nims
index ff37614..dfd3773 100644
--- a/tests/fuzzing/config.nims
+++ b/tests/fuzzing/config.nims
@@ -7,6 +7,7 @@ proc aflSwitches() =
   switch("out", "fuzz-afl")
 
 proc libFuzzerSwitches() =
+  switch("define", "libFuzzer")
   switch("noMain", "")
   switch("cc", "clang")
   switch("passC", "-fsanitize=fuzzer,address")
diff --git a/tests/fuzzing/fuzz_helpers.nim b/tests/fuzzing/fuzz_helpers.nim
index 94ee2a3..a65dc52 100644
--- a/tests/fuzzing/fuzz_helpers.nim
+++ b/tests/fuzzing/fuzz_helpers.nim
@@ -44,7 +44,7 @@ type
     clangFast = aflClangFast
 
 proc aflCompile*(target: string, c: Compiler) =
-  let aflOptions = &"-d:standalone -d:noSignalHandler {$c}"
+  let aflOptions = &"-d:afl -d:noSignalHandler {$c}"
   let compileCmd = &"nim c {defaultFlags} {aflOptions} {target.quoteShell()}"
   exec compileCmd
 
@@ -66,7 +66,7 @@ proc aflExec*(target: string, inputDir: string, resultsDir: string,
   exec fuzzCmd
 
 proc libFuzzerCompile*(target: string) =
-  let libFuzzerOptions = &"--noMain {libFuzzerClang}"
+  let libFuzzerOptions = &"-d:libFuzzer --noMain {libFuzzerClang}"
   let compileCmd = &"nim c {defaultFlags} {libFuzzerOptions} {target.quoteShell()}"
   exec compileCmd
 
diff --git a/tests/fuzzing/fuzztest.nim b/tests/fuzzing/fuzztest.nim
index 847a13d..232b12d 100644
--- a/tests/fuzzing/fuzztest.nim
+++ b/tests/fuzzing/fuzztest.nim
@@ -3,7 +3,7 @@ import streams, posix, strutils, chronicles, macros, stew/ranges/ptr_arith
 template fuzz(body) =
   # For code we want to fuzz, SIGSEGV is needed on unwanted exceptions.
   # However, this is only needed when fuzzing with afl.
-  when defined(standalone):
+  when defined(afl):
     try:
       body
     except Exception as e:
@@ -29,7 +29,7 @@ proc NimMain() {.importc: "NimMain".}
 
 # The default init, gets redefined when init template is used.
 template initImpl(): untyped =
-  when defined(standalone):
+  when not defined(libFuzzer):
     discard
   else:
     proc fuzzerInit(): cint {.exportc: "LLVMFuzzerInitialize".} =
@@ -46,7 +46,7 @@ template init*(body: untyped) =
   ## For libFuzzer this will only be run once. So only put data which is
   ## stateless or make sure everything gets properply reset for each new run in
   ## the test block.
-  when defined(standalone):
+  when not defined(libFuzzer):
     template initImpl(): untyped = fuzz: `body`
   else:
     template initImpl() =
@@ -64,7 +64,7 @@ template test*(body: untyped): untyped =
   ## contains the payload provided by the fuzzer.
   mixin initImpl
   initImpl()
-  when defined(standalone):
+  when not defined(libFuzzer):
     var payload {.inject.} = readStdin()
 
     fuzz: `body`
@@ -76,8 +76,6 @@ template test*(body: untyped): untyped =
 
       `body`
 
-# var aflClangFast {.importc: "__AFL_HAVE_MANUAL_CONTROL", noDecl.}: int
-
 when defined(clangfast):
   ## Can be used for deferred instrumentation.
   ## Should be placed on a suitable location in the code where the delayed
diff --git a/tests/fuzzing/readme.md b/tests/fuzzing/readme.md
index b6b0fa3..2e29df0 100644
--- a/tests/fuzzing/readme.md
+++ b/tests/fuzzing/readme.md
@@ -92,9 +92,9 @@ nim fuzz.nims libFuzzer testcase.nim
 #### Compiling
 With gcc:
 ```sh
-nim c -d:standalone -d:release -d:chronicles_log_level=fatal -d:noSignalHandler --cc=gcc --gcc.exe=afl-gcc --gcc.linkerexe=afl-gcc testcase.nim
+nim c -d:afl -d:release -d:chronicles_log_level=fatal -d:noSignalHandler --cc=gcc --gcc.exe=afl-gcc --gcc.linkerexe=afl-gcc testcase.nim
 ```
-The `standalone` define is specifically required for the `init` and `test`
+The `afl` define is specifically required for the `init` and `test`
 templates.
 
 You typically want to fuzz in `-d:release` and probably also want to lower down
@@ -108,9 +108,9 @@ nim c build_afl testcase.nim
 With clang:
 ```sh
 # afl-clang
-nim c -d:standalone -d:noSignalHandler --cc=clang --clang.exe=afl-clang --clang.linkerexe=afl-clang ftestcase.nim
+nim c -d:afl -d:noSignalHandler --cc=clang --clang.exe=afl-clang --clang.linkerexe=afl-clang ftestcase.nim
 # afl-clang-fast
-nim c -d:standalone -d:noSignalHandler --cc=clang --clang.exe=afl-clang-fast --clang.linkerexe=afl-clang-fast testcase.nim
+nim c -d:afl -d:noSignalHandler --cc=clang --clang.exe=afl-clang-fast --clang.linkerexe=afl-clang-fast testcase.nim
 ```
 
 #### Starting the Fuzzer
@@ -135,17 +135,26 @@ afl-fuzz -i input -o results -S fuzzer03 -- ./testcase
 # add more if needed
 ```
 
-When compiled with `-d:standalone` the resulting application can also be run
+When compiled with `-d:afl` the resulting application can also be run
 manually by providing it input data, e.g.:
 ```sh
-cat testfile | ./testcase
+./testcase < testfile
 ```
 
+During debugging you might not want the testcase to generate a segmentation
+fault on exceptions. You can do this by rebuilding the test without the `-d:afl`
+flag. Changing to `-d:debug` will also help but might also change the
+behaviour.
+
 ### Manually with libFuzzer
 #### Compiling
 ```sh
-nim c -d:release -d:chronicles_log_level=fatal --noMain --cc=clang --passC="-fsanitize=fuzzer" --passL="-fsanitize=fuzzer" testcase.nim
+nim c -d:libFuzzer -d:release -d:chronicles_log_level=fatal --noMain --cc=clang --passC="-fsanitize=fuzzer" --passL="-fsanitize=fuzzer" testcase.nim
 ```
+
+The `libFuzzer` define is specifically required for the `init` and `test`
+templates.
+
 You typically want to fuzz in `-d:release` and probably also want to lower down
 the logging. But this is not strictly necessary.
 
@@ -180,14 +189,16 @@ The `init` template, when used with **afl**, is only cosmetic. It will be
 run before each test block, compared to libFuzzer, where it will be run only
 once.
 
-In case of using afl with `alf-clang-fast` you can make use of `aflInit()` and
-`aflLoop()` calls.
+In case of using afl with `alf-clang-fast` you can make use of `aflInit()` proc
+and `aflLoop()` template.
 
 `aflInit()` will allow using what is called deferred instrumentation. Basically,
 the forking of the process will only happen after this call, where normally it
 is done right before `main()`.
 
-`aflLoop(cint)` will allow for (experimental) persistant mode. This is more
-comparable with libFuzzer.
+`aflLoop:` will allow for (experimental) persistant mode. It will run the test
+in loop (1000 iterations) with different payloads. This is more comparable with
+libFuzzer.
 
-These calls are enabled with `-d:clangfast`.
+These calls are enabled with `-d:clangfast`, and have to be manually added.
+They are currently not part of the `test` or `init` templates.