diff --git a/configure.ac b/configure.ac
index b48942b..c5cd6e7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,7 +37,7 @@
 )
 
 # Checks for typedefs, structures, and compiler characteristics.
-AX_CXX_COMPILE_STDCXX_17([noext])
+AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
 AX_APPEND_COMPILE_FLAGS([-Wall -Werror], [CFLAGS])
 AX_APPEND_COMPILE_FLAGS([-Wall -Werror], [CXXFLAGS])