diff --git a/acinclude.m4 b/acinclude.m4
index ec7d20d..844f118 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -178,7 +178,7 @@ AC_DEFUN([CURL_CHECK_NONBLOCKING_SOCKET],
 #  define PLATFORM_SUNOS4
 # endif
 #endif
-#if (defined(_AIX) || defined(__xlC__)) && !defined(_AIX4)
+#if (defined(_AIX) || defined(__xlC__)) && !defined(_AIX41)
 # define PLATFORM_AIX_V3
 #endif