diff --git a/velox/expression/fuzzer/ExpressionFuzzerTest.cpp b/velox/expression/fuzzer/ExpressionFuzzerTest.cpp
index ece09fa4bf4e..cb3a186e5abf 100644
--- a/velox/expression/fuzzer/ExpressionFuzzerTest.cpp
+++ b/velox/expression/fuzzer/ExpressionFuzzerTest.cpp
@@ -113,7 +113,8 @@ int main(int argc, char** argv) {
       // from_unixtime can generate timestamps out of the supported range that
       // make other functions throw VeloxRuntimeErrors.
       "from_unixtime",
-  };
+      // JSON not supported, Real doesn't match exactly, etc.
+      "array_join"};
   size_t initialSeed = FLAGS_seed == 0 ? std::time(nullptr) : FLAGS_seed;
 
   std::unordered_map<std::string, std::shared_ptr<ArgTypesGenerator>>
diff --git a/velox/functions/prestosql/registration/ArrayFunctionsRegistration.cpp b/velox/functions/prestosql/registration/ArrayFunctionsRegistration.cpp
index b2e6f0d23279..a2b8ecf639af 100644
--- a/velox/functions/prestosql/registration/ArrayFunctionsRegistration.cpp
+++ b/velox/functions/prestosql/registration/ArrayFunctionsRegistration.cpp
@@ -200,6 +200,7 @@ void registerArrayFunctions(const std::string& prefix) {
   registerArrayJoinFunctions<Timestamp>(prefix);
   registerArrayJoinFunctions<Date>(prefix);
   registerArrayJoinFunctions<Json>(prefix);
+  registerArrayJoinFunctions<UnknownValue>(prefix);
 
   registerFunction<ArrayAverageFunction, double, Array<double>>(
       {prefix + "array_average"});
diff --git a/velox/functions/prestosql/tests/ArrayJoinTest.cpp b/velox/functions/prestosql/tests/ArrayJoinTest.cpp
index 0498c4eff5c8..e07e690db222 100644
--- a/velox/functions/prestosql/tests/ArrayJoinTest.cpp
+++ b/velox/functions/prestosql/tests/ArrayJoinTest.cpp
@@ -268,4 +268,16 @@ TEST_F(ArrayJoinTest, jsonTest) {
       false,
       true);
 }
+
+TEST_F(ArrayJoinTest, unknownTest) {
+  testArrayJoinNoReplacement<UnknownValue>(
+      {std::nullopt, std::nullopt, std::nullopt}, ","_sv, ""_sv);
+
+  testArrayJoinReplacement<UnknownValue>(
+      {std::nullopt, std::nullopt, std::nullopt},
+      ","_sv,
+      "null"_sv,
+      "null,null,null"_sv);
+}
+
 } // namespace