--- old/src/hotspot/cpu/x86/globals_x86.hpp	2019-10-17 17:31:26.000000000 -0400
+++ new/src/hotspot/cpu/x86/globals_x86.hpp	2019-10-17 17:31:25.000000000 -0400
@@ -94,9 +94,20 @@
 
 #if defined(_LP64) || defined(_WINDOWS)
 define_pd_global(bool, ThreadLocalHandshakes, true);
+// ObjectMonitor ref_count is implemented in LP64 C2 fast_lock()
+// and fast_unlock() so we don't need the handshake by default.
+#ifdef _LP64
+define_pd_global(bool, HandshakeAfterDeflateIdleMonitors, false);
+#else
+define_pd_global(bool, HandshakeAfterDeflateIdleMonitors, true);
+#endif
 #else
 // get_thread() is slow on linux 32 bit, therefore off by default
 define_pd_global(bool, ThreadLocalHandshakes, false);
+// ObjectMonitor ref_count not implemented in C2 fast_lock() or
+// fast_unlock() so use a handshake for safety.
+// Will use a safepoint instead of a handshake on this platform.
+define_pd_global(bool, HandshakeAfterDeflateIdleMonitors, true);
 #endif
 
 #define ARCH_FLAGS(develop, \