diff --git a/sys/alpha/include/varargs.h b/sys/alpha/include/varargs.h
index a5a997d95340..f6a47f83ca6a 100644
--- a/sys/alpha/include/varargs.h
+++ b/sys/alpha/include/varargs.h
@@ -48,7 +48,11 @@
 
 #include <sys/_types.h>
 
+#ifndef _VA_LIST_DECLARED
+#define	_VA_LIST_DECLARED
 typedef	__va_list	va_list;
+#endif
+
 typedef int __builtin_va_alist_t __attribute__((__mode__(__word__)));
 
 #define	va_alist		__builtin_va_alist
diff --git a/sys/amd64/include/varargs.h b/sys/amd64/include/varargs.h
index 5d8511e9a9ab..ce53976e975e 100644
--- a/sys/amd64/include/varargs.h
+++ b/sys/amd64/include/varargs.h
@@ -47,7 +47,11 @@
 
 #include <sys/_types.h>
 
+#ifndef _VA_LIST_DECLARED
+#define	_VA_LIST_DECLARED
 typedef	__va_list	va_list;
+#endif
+
 typedef int __builtin_va_alist_t __attribute__((__mode__(__word__)));
 
 #define	va_alist		__builtin_va_alist
diff --git a/sys/i386/include/varargs.h b/sys/i386/include/varargs.h
index 5d8511e9a9ab..ce53976e975e 100644
--- a/sys/i386/include/varargs.h
+++ b/sys/i386/include/varargs.h
@@ -47,7 +47,11 @@
 
 #include <sys/_types.h>
 
+#ifndef _VA_LIST_DECLARED
+#define	_VA_LIST_DECLARED
 typedef	__va_list	va_list;
+#endif
+
 typedef int __builtin_va_alist_t __attribute__((__mode__(__word__)));
 
 #define	va_alist		__builtin_va_alist
diff --git a/sys/ia64/include/varargs.h b/sys/ia64/include/varargs.h
index fcc78c248e0c..f45b5d71719a 100644
--- a/sys/ia64/include/varargs.h
+++ b/sys/ia64/include/varargs.h
@@ -45,7 +45,11 @@
 
 #include <sys/_types.h>
 
+#ifndef _VA_LIST_DECLARED
+#define	_VA_LIST_DECLARED
 typedef	__va_list	va_list;
+#endif
+
 typedef int __builtin_va_alist_t __attribute__((__mode__(__word__)));
 
 #define	va_alist		__builtin_va_alist
diff --git a/sys/powerpc/include/varargs.h b/sys/powerpc/include/varargs.h
index 6ac271a9d723..26d8a9327154 100644
--- a/sys/powerpc/include/varargs.h
+++ b/sys/powerpc/include/varargs.h
@@ -35,7 +35,11 @@
 
 #include <sys/_types.h>
 
+#ifndef _VA_LIST_DECLARED
+#define	_VA_LIST_DECLARED
 typedef	__va_list	va_list;
+#endif
+
 typedef int __builtin_va_alist_t __attribute__((__mode__(__word__)));
 
 #define	va_alist		__builtin_va_alist
diff --git a/sys/sparc64/include/varargs.h b/sys/sparc64/include/varargs.h
index a93b89f105d1..7ee2a589554e 100644
--- a/sys/sparc64/include/varargs.h
+++ b/sys/sparc64/include/varargs.h
@@ -53,7 +53,11 @@
 
 #include <sys/_types.h>
 
+#ifndef _VA_LIST_DECLARED
+#define	_VA_LIST_DECLARED
 typedef	__va_list	va_list;
+#endif
+
 typedef int __builtin_va_alist_t __attribute__((__mode__(__word__)));
 
 #define	va_alist		__builtin_va_alist