diff --git a/core/definitions.mk b/core/definitions.mk
index 63b123e..78a7091 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2531,6 +2531,7 @@
 $(if $(filter $(1),$(PLATFORM_VERSION_CODENAME)),10000,$(1))
 endef
 
+# --add-opens is required because desugar reflects via java.lang.invoke.MethodHandles.Lookup
 define desugar-classes-jar
 @echo Desugar: $@
 @mkdir -p $(dir $@)
@@ -2538,6 +2539,7 @@
 @rm -rf $(dir $@)/desugar_dumped_classes
 @mkdir $(dir $@)/desugar_dumped_classes
 $(hide) java \
+    $(if $(EXPERIMENTAL_USE_OPENJDK9),--add-opens java.base/java.lang.invoke=ALL-UNNAMED,) \
     -Djdk.internal.lambda.dumpProxyClasses=$(abspath $(dir $@))/desugar_dumped_classes \
     -jar $(DESUGAR) \
     $(addprefix --bootclasspath_entry ,$(call desugar-bootclasspath,$(PRIVATE_BOOTCLASSPATH))) \