diff --git a/configure.ac b/configure.ac
index 28015d005..34b8354cd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -422,6 +422,9 @@ if test "x$CXXFLAGS_overridden" = "xno"; then
   AX_CHECK_COMPILE_FLAG([-Wdeprecated-copy],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-deprecated-copy"],,[[$CXXFLAG_WERROR]])
 fi
 
+dnl Don't allow extended (non-ASCII) symbols in identifiers. This is easier for code review.
+AX_CHECK_COMPILE_FLAG([-fno-extended-identifiers],[[CXXFLAGS="$CXXFLAGS -fno-extended-identifiers"]],,[[$CXXFLAG_WERROR]])
+
 enable_sse42=no
 enable_sse41=no
 enable_avx2=no