diff --git a/src/s/aix4.h b/src/s/aix4.h
index 9f04d5aa25c..cdba4869a45 100644
--- a/src/s/aix4.h
+++ b/src/s/aix4.h
@@ -13,3 +13,7 @@
 /* Dave Love <d.love@dl.ac.uk> reported this as needed on AIX 4.1.
    It is just a guess which versions of AIX need this definition.  */
 #define HAVE_WAIT_HEADER
+
+/* Specify the type that the 3rd arg of `accept' points to.
+   It is just a guess which versions of AIX need this definition.  */
+#define SOCKLEN_TYPE int