diff --git a/Makefile b/Makefile
index 9bb24f1..297d97c 100644
--- a/Makefile
+++ b/Makefile
@@ -381,7 +381,7 @@
 # AIX 5.1 only
 ifeq ($(TARGET),aix51)
   set_target_defaults = $(call default_opts, \
-    USE_POLL USE_LIBCRYPT USE_OBSOLETE_LINKER)
+    USE_POLL USE_LIBCRYPT USE_OBSOLETE_LINKER USE_PRIVATE_CACHE)
   TARGET_CFLAGS   = -Dss_family=__ss_family -Dip6_hdr=ip6hdr -DSTEVENS_API -D_LINUX_SOURCE_COMPAT -Dunsetenv=my_unsetenv
   DEBUG_CFLAGS    =
 endif