diff --git a/MultiSource/Applications/ClamAV/CMakeLists.txt b/MultiSource/Applications/ClamAV/CMakeLists.txt
--- a/MultiSource/Applications/ClamAV/CMakeLists.txt
+++ b/MultiSource/Applications/ClamAV/CMakeLists.txt
@@ -23,7 +23,7 @@
   list(APPEND CPPFLAGS -DC_DARWIN)
 endif()
 if(TARGET_OS STREQUAL "AIX")
-  list(APPEND CPPFLAGS -DC_AIX)
+  list(APPEND CPPFLAGS -DC_AIX -D_XOPEN_SOURCE=600)
 endif()
 if(TARGET_OS STREQUAL "IRIX")
   list(APPEND CPPFLAGS -DC_IRIX)
diff --git a/MultiSource/Applications/ClamAV/Makefile b/MultiSource/Applications/ClamAV/Makefile
--- a/MultiSource/Applications/ClamAV/Makefile
+++ b/MultiSource/Applications/ClamAV/Makefile
@@ -73,7 +73,7 @@
    CPPFLAGS += -DC_DARWIN
 endif
 ifeq ($(TARGET_OS),AIX)
-   CPPFLAGS += -DC_AIX
+   CPPFLAGS += -DC_AIX -D_XOPEN_SOURCE=600
 endif
 ifeq ($(TARGET_OS), IRIX)
    CPPFLAGS += -DC_IRIX
diff --git a/MultiSource/Applications/ClamAV/others.h b/MultiSource/Applications/ClamAV/others.h
--- a/MultiSource/Applications/ClamAV/others.h
+++ b/MultiSource/Applications/ClamAV/others.h
@@ -26,6 +26,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 #include "cltypes.h"
 
 #include "clamav.h"
diff --git a/MultiSource/Applications/ClamAV/shared_cfgparser.c b/MultiSource/Applications/ClamAV/shared_cfgparser.c
--- a/MultiSource/Applications/ClamAV/shared_cfgparser.c
+++ b/MultiSource/Applications/ClamAV/shared_cfgparser.c
@@ -24,6 +24,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 #include <ctype.h>
 
 #include "cfgparser.h"
diff --git a/MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt b/MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt
--- a/MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt
+++ b/MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt
@@ -3,6 +3,11 @@
 list(APPEND CXXFLAGS -Wno-implicit-function-declaration)
 check_function_exists(re_comp HAVE_RE_COMP)
 
+if(TARGET_OS STREQUAL "AIX")
+  list(APPEND CFLAGS -D_XOPEN_SOURCE=600)
+  list(APPEND CXXFLAGS -D_XOPEN_SOURCE=600)
+endif()
+
 if(HAVE_RE_COMP)
   if(TARGET_OS STREQUAL "SunOS")
     list(APPEND LDFLAGS -lsocket -lnsl)
diff --git a/MultiSource/Benchmarks/Prolangs-C/archie-client/Makefile b/MultiSource/Benchmarks/Prolangs-C/archie-client/Makefile
--- a/MultiSource/Benchmarks/Prolangs-C/archie-client/Makefile
+++ b/MultiSource/Benchmarks/Prolangs-C/archie-client/Makefile
@@ -15,3 +15,8 @@
 ifeq ($(TARGET_OS),SunOS)
 LDFLAGS += -lsocket -lnsl
 endif
+
+ifeq ($(TARGET_OS),AIX)
+CFLAGS += -D_XOPEN_SOURCE=600
+CXXFLAGS += -D_XOPEN_SOURCE=600
+endif