diff --git a/configure.in b/configure.in
index 20102d4e..b65d1558 100644
--- a/configure.in
+++ b/configure.in
@@ -108,14 +108,14 @@ AC_HEADER_TIME
 
 # Required header files
 AC_CHECK_HEADERS([ \
-	fcntl.h inttypes.h netdb.h netinet/in.h netinet/in_systm.h stdlib.h \
-	string.h strings.h sys/socket.h sys/time.h unistd.h \
+	fcntl.h netdb.h netinet/in.h netinet/in_systm.h stdlib.h string.h \
+	strings.h sys/socket.h sys/time.h unistd.h \
 	],,AC_MSG_ERROR([required C header missing!]))
 
 # Optional header files
 AC_CHECK_HEADERS([ \
-	arpa/inet.h malloc.h netinet/ip.h stdbool.h stddef.h stdint.h \
-	varargs.h \
+	arpa/inet.h inttypes.h malloc.h netinet/ip.h stdbool.h stddef.h \
+	stdint.h varargs.h \
 	])
 
 # -- Datatypes --