diff --git a/llvm/unittests/ExecutionEngine/Orc/RPCUtilsTest.cpp b/llvm/unittests/ExecutionEngine/Orc/RPCUtilsTest.cpp
index 87c98ad1dfbb..9bf861a595b6 100644
--- a/llvm/unittests/ExecutionEngine/Orc/RPCUtilsTest.cpp
+++ b/llvm/unittests/ExecutionEngine/Orc/RPCUtilsTest.cpp
@@ -219,23 +219,25 @@ TEST_F(DummyRPC, TestSerialization) {
 }
 
 // Test the synchronous call API.
-TEST_F(DummyRPC, TestSynchronousCall) {
-  Queue Q1, Q2;
-  QueueChannel C1(Q1, Q2);
-  QueueChannel C2(Q2, Q1);
-
-  auto ServerResult =
-    std::async(std::launch::async,
-      [&]() {
-        return expect<IntInt>(C2, [&](int32_t V) { return V; });
-      });
-
-  auto ValOrErr = callST<IntInt>(C1, 42);
-
-  EXPECT_FALSE(!!ServerResult.get())
-    << "Server returned an error.";
-  EXPECT_TRUE(!!ValOrErr)
-    << "callST returned an error.";
-  EXPECT_EQ(*ValOrErr, 42)
-    << "Incorrect callST<IntInt> result";
-}
+// FIXME: Re-enable once deadlock encountered on S390 has been debugged / fixed,
+//        see http://lab.llvm.org:8011/builders/clang-s390x-linux/builds/3459
+// TEST_F(DummyRPC, TestSynchronousCall) {
+//   Queue Q1, Q2;
+//   QueueChannel C1(Q1, Q2);
+//   QueueChannel C2(Q2, Q1);
+//
+//   auto ServerResult =
+//     std::async(std::launch::async,
+//       [&]() {
+//         return expect<IntInt>(C2, [&](int32_t V) { return V; });
+//       });
+//
+//   auto ValOrErr = callST<IntInt>(C1, 42);
+//
+//   EXPECT_FALSE(!!ServerResult.get())
+//     << "Server returned an error.";
+//   EXPECT_TRUE(!!ValOrErr)
+//     << "callST returned an error.";
+//   EXPECT_EQ(*ValOrErr, 42)
+//     << "Incorrect callST<IntInt> result";
+// }