diff --git a/config.h.cmake.in b/config.h.cmake.in
index 19b79bc..25273ac 100644
--- a/config.h.cmake.in
+++ b/config.h.cmake.in
@@ -62,9 +62,6 @@
 /* Enable --x509-username-field feature */
 #cmakedefine ENABLE_X509ALTUSERNAME
 
-/* Compiler supports anonymous unions */
-#define HAVE_ANONYMOUS_UNION_SUPPORT
-
 /* Define to 1 if you have the <arpa/inet.h> header file. */
 #cmakedefine HAVE_ARPA_INET_H 1
 
@@ -139,9 +136,6 @@
 /* Define to 1 if you have the `getpwnam' function. */
 #cmakedefine HAVE_GETPWNAM
 
-/* Define to 1 if you have the `getrlimit' function. */
-#undef HAVE_GETRLIMIT
-
 /* Define to 1 if you have the `getsockname' function. */
 #cmakedefine HAVE_GETSOCKNAME
 
@@ -235,8 +229,6 @@
 /* Define to 1 if you have the <pwd.h> header file. */
 #cmakedefine HAVE_PWD_H
 
-/* Define to 1 if you have the `readv' function. */
-#undef HAVE_READV
 
 /* Define to 1 if you have the `recvmsg' function. */
 #cmakedefine HAVE_RECVMSG
@@ -383,9 +375,6 @@
 /* Define to 1 if you have the <vfork.h> header file. */
 #undef HAVE_VFORK_H
 
-/* Define to 1 if you have the `vsnprintf' function. */
-#undef HAVE_VSNPRINTF
-
 /* we always assume a recent mbed TLS version */
 #define HAVE_MBEDTLS_PSA_CRYPTO_H 1
 #define HAVE_MBEDTLS_SSL_TLS_PRF 1
diff --git a/configure.ac b/configure.ac
index 84eaad6..055b2a7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -561,28 +561,6 @@
 	,
 	[[${SOCKET_INCLUDES}]]
 )
-AC_MSG_CHECKING([anonymous union support])
-AC_COMPILE_IFELSE(
-	[AC_LANG_PROGRAM(
-		[[
-			struct mystruct {
-			  union {
-			    int m1;
-			    char m2;
-			  };
-			};
-		]],
-		[[
-			struct mystruct s;
-			s.m1 = 1; s.m2 = 2;
-		]]
-	)],
-	[
-		AC_MSG_RESULT([yes])
-		AC_DEFINE([HAVE_ANONYMOUS_UNION_SUPPORT], [], [Compiler supports anonymous unions])
-	],
-	[AC_MSG_RESULT([no])]
-)
 
 saved_LDFLAGS="$LDFLAGS"
 LDFLAGS="$LDFLAGS -Wl,--wrap=exit"
@@ -655,7 +633,7 @@
 AC_CHECK_FUNCS([ \
 	daemon chroot getpwnam setuid nice system dup dup2 \
 	syslog openlog mlockall getrlimit getgrnam setgid \
-	setgroups flock readv writev time gettimeofday \
+	setgroups flock time gettimeofday \
 	setsid chdir \
 	chsize ftruncate execve getpeereid basename dirname access \
 	epoll_create strsep \