diff --git a/configure.ac b/configure.ac
index 9ee281a16..af41f5e3a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -24,6 +24,9 @@ LT_INIT
 
 AC_HEADER_STDC
 
+dnl fail hard when includes statements are missing
+CFLAGS+=" -Werror=implicit-function-declaration"
+
 PKG_PROG_PKG_CONFIG
 
 AC_ARG_ENABLE([server],
diff --git a/util/ipa_pwd_ntlm.c b/util/ipa_pwd_ntlm.c
index f7099811e..263816dc5 100644
--- a/util/ipa_pwd_ntlm.c
+++ b/util/ipa_pwd_ntlm.c
@@ -26,6 +26,7 @@
 
 #include <stdlib.h>
 #include <stdbool.h>
+#include <string.h>
 #include <iconv.h>
 #include <openssl/md4.h>