diff --git a/libc/tools/zoneinfo/update-tzdata.py b/libc/tools/zoneinfo/update-tzdata.py
index 4847356..d5788af 100755
--- a/libc/tools/zoneinfo/update-tzdata.py
+++ b/libc/tools/zoneinfo/update-tzdata.py
@@ -140,7 +140,7 @@
 
   # Regenerate the .dat file.
   os.chdir(icu_working_dir)
-  subprocess.check_call(['make', '-j32'])
+  subprocess.check_call(['make', 'INCLUDE_UNI_CORE_DATA=1', '-j32'])
 
   # Copy the .dat file to its ultimate destination.
   icu_dat_data_dir = '%s/stubdata' % icu_dir