diff --git a/icu4c/source/config/mh-os390 b/icu4c/source/config/mh-os390
index 97494021b2b..aa66db1cb8a 100644
--- a/icu4c/source/config/mh-os390
+++ b/icu4c/source/config/mh-os390
@@ -14,41 +14,24 @@
 #                                                                 #
 #   export OS390BATCH=1                                           #
 #                                                                 #
-# Also, search for the LOADMOD variable and set it to your        #
-# LOADMOD dataset. Make sure you have at least UPDATE access to   #
-# the dataset.                                                    #
-#                                                                 #
-#                                                                 #
 # To build a version of ICU which uses IEEE Floating point        #
 #                                                                 #
 #   export IEEE390=1                                              #
 #                                                                 #
-# To enable DEBUG mode, just type                                 #
-# export DEBUG=1                                                  #
-# on your shell (bash assumed) before building.                   #
-# To cancel DEBUG mode, type                                      #
-# unset DEBUG                                                     #
-# on your shell command line.                                     #
 ###################################################################
 
-ifeq (${DEBUG}, 1)
-ICU_BUILD_OPTIONS = -g
-else
-ICU_BUILD_OPTIONS = -2
-endif
-
 ifeq (${IEEE390}, 1)
 ICU_IEEE          = -Wc,"float(ieee)" -DIEEE_ON
 else
 ICU_IEEE          = 
 endif
 
-CFLAGS390=      -Wc,"langlvl(extended),spill(2000)" $(ICU_BUILD_OPTIONS) $(ICU_IEEE) -Wc,dll,expo
+CFLAGS390=      -Wc,"langlvl(extended),spill(2000)"  $(ICU_IEEE) -Wc,dll,expo
 ## OS390BATCH
 ifeq (${OS390BATCH},1)
-DEFS390=        -D_OPEN_THREADS -D_XOPEN_SOURCE_EXTENDED -DOS390BATCH
+DEFS390=        -D_OPEN_THREADS -D_XOPEN_SOURCE_EXTENDED -DOS390BATCH -D_SHARE_EXT_VARS
 else
-DEFS390=        -D_OPEN_THREADS -D_XOPEN_SOURCE_EXTENDED
+DEFS390=        -D_OPEN_THREADS -D_XOPEN_SOURCE_EXTENDED -D_SHARE_EXT_VARS
 endif
 ARFLAGS=        -cr