diff --git a/ext/standard/config.m4 b/ext/standard/config.m4
index 4b687b3df5f29..58b9c5e658a41 100644
--- a/ext/standard/config.m4
+++ b/ext/standard/config.m4
@@ -407,6 +407,8 @@ if test "$PHP_PASSWORD_ARGON2" != "no"; then
   PKG_CHECK_MODULES([ARGON2], [libargon2])
   PHP_EVAL_INCLINE($ARGON2_CFLAGS)
   PHP_EVAL_LIBLINE($ARGON2_LIBS)
+
+  AC_DEFINE(HAVE_ARGON2LIB, 1, [ ])
 fi
 
 dnl