--- a/lib/crypto_backend/argon2/Makemodule.am
+++ b/lib/crypto_backend/argon2/Makemodule.am
@@ -1,6 +1,6 @@
 noinst_LTLIBRARIES += libargon2.la

-libargon2_la_CFLAGS = $(AM_CFLAGS) -std=c89 -pthread -O3
+libargon2_la_CFLAGS = $(AM_CFLAGS) -pthread -O3
 libargon2_la_CPPFLAGS = $(AM_CPPFLAGS) \
 	-I lib/crypto_backend/argon2 \
 	-I lib/crypto_backend/argon2/blake2