diff --git a/src/libfuzzer/libfuzzer_mutator.cc b/src/libfuzzer/libfuzzer_mutator.cc
index 34d144c..b671fd4 100644
--- a/src/libfuzzer/libfuzzer_mutator.cc
+++ b/src/libfuzzer/libfuzzer_mutator.cc
@@ -14,6 +14,8 @@
 
 #include "src/libfuzzer/libfuzzer_mutator.h"
 
+#include <sanitizer/msan_interface.h>
+
 #include <string.h>
 
 #include <algorithm>
@@ -64,6 +66,7 @@ template <class T>
 T MutateValue(T v) {
   size_t size =
       LLVMFuzzerMutate(reinterpret_cast<uint8_t*>(&v), sizeof(v), sizeof(v));
+  __msan_unpoison(reinterpret_cast<uint8_t*>(&v), size);
   memset(reinterpret_cast<uint8_t*>(&v) + size, 0, sizeof(v) - size);
   return v;
 }
@@ -93,6 +96,7 @@ std::string Mutator::MutateString(const std::string& value,
   result.resize(std::max(1, new_size));
   result.resize(LLVMFuzzerMutate(reinterpret_cast<uint8_t*>(&result[0]),
                                  value.size(), result.size()));
+  __msan_unpoison(reinterpret_cast<uint8_t*>(&result[0]), result.size());
   return result;
 }
 
