diff --git a/expat/CMakeLists.txt b/expat/CMakeLists.txt
index 79287b5d..e298d3eb 100644
--- a/expat/CMakeLists.txt
+++ b/expat/CMakeLists.txt
@@ -778,7 +778,7 @@ if(EXPAT_BUILD_FUZZERS)
         GIT_REPOSITORY https://github.com/google/libprotobuf-mutator.git
         GIT_TAG 50ef9159bb838931d83e5bbd77eeec05fc50f57d  # v1.1-7-g50ef915, last before commit "Switch to requires_utf8_validation"
         CMAKE_ARGS -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
-        CMAKE_CACHE_ARGS -DCMAKE_C_COMPILER:FILEPATH=${CMAKE_C_COMPILER} -DCMAKE_CXX_COMPILER:FILEPATH=${CMAKE_CXX_COMPILER}
+        CMAKE_CACHE_ARGS -DCMAKE_C_COMPILER:FILEPATH=${CMAKE_C_COMPILER} -DCMAKE_CXX_COMPILER:FILEPATH=${CMAKE_CXX_COMPILER} -DLIB_PROTO_MUTATOR_TESTING:BOOL=OFF
         BUILD_BYPRODUCTS ${ProtobufMutator_LIBRARIES}
         PATCH_COMMAND sed -e "s,-Werror, ," -e "s,CMAKE_CXX_STANDARD [0-9]\\+,CMAKE_CXX_STANDARD 17," -i.bak ${ProtobufMutator_PATH}/CMakeLists.txt
         UPDATE_COMMAND true