--- old/src/hotspot/cpu/aarch64/globals_aarch64.hpp	2020-02-03 17:41:30.000000000 -0500
+++ new/src/hotspot/cpu/aarch64/globals_aarch64.hpp	2020-02-03 17:41:29.000000000 -0500
@@ -71,6 +71,10 @@
 // Clear short arrays bigger than one word in an arch-specific way
 define_pd_global(intx, InitArrayShortSize, BytesPerLong);
 
+// ObjectMonitor ref_count not implemented in C2 fast_lock() or
+// fast_unlock() so use a handshake for safety.
+define_pd_global(bool, HandshakeAfterDeflateIdleMonitors, true);
+
 #if defined(COMPILER1) || defined(COMPILER2)
 define_pd_global(intx, InlineSmallCode,          1000);
 #endif