--- old/src/hotspot/cpu/s390/globals_s390.hpp	2019-10-17 17:28:30.000000000 -0400
+++ new/src/hotspot/cpu/s390/globals_s390.hpp	2019-10-17 17:28:29.000000000 -0400
@@ -80,6 +80,9 @@
 define_pd_global(intx, InitArrayShortSize, 1*BytesPerLong);
 
 define_pd_global(bool, ThreadLocalHandshakes, true);
+// ObjectMonitor ref_count not implemented in C2 fast_lock() or
+// fast_unlock() so use a handshake for safety.
+define_pd_global(bool, HandshakeAfterDeflateIdleMonitors, true);
 
 #define ARCH_FLAGS(develop,      \
                    product,      \