diff --git a/src/s/aix4.h b/src/s/aix4.h
new file mode 100644
index 00000000000..ac2c0bd380c
--- /dev/null
+++ b/src/s/aix4.h
@@ -0,0 +1,4 @@
+#include <aix3-2-5.h>
+
+/* AIX 4 does not have HFT any more.  */
+#undef AIXHFT