--- old/src/hotspot/cpu/s390/globals_s390.hpp	2019-12-11 14:51:55.000000000 -0500
+++ new/src/hotspot/cpu/s390/globals_s390.hpp	2019-12-11 14:51:54.000000000 -0500
@@ -77,6 +77,9 @@
 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,      \