--- old/src/hotspot/cpu/s390/globals_s390.hpp	2020-02-03 17:38:46.000000000 -0500
+++ new/src/hotspot/cpu/s390/globals_s390.hpp	2020-02-03 17:38:45.000000000 -0500
@@ -76,6 +76,10 @@
 // 8146801 (Short Array Allocation): No performance work done here yet.
 define_pd_global(intx, InitArrayShortSize, 1*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);
+
 #define ARCH_FLAGS(develop,      \
                    product,      \
                    diagnostic,   \