diff --git a/lib/libc/tests/stdio/Makefile b/lib/libc/tests/stdio/Makefile
--- a/lib/libc/tests/stdio/Makefile
+++ b/lib/libc/tests/stdio/Makefile
@@ -38,9 +38,15 @@
 LIBADD.printfloat_test+= m
 LIBADD.scanfloat_test+=  m
 
+# Older toolchains won't understand C23 %b, %wN, %wfN
+PROG_OVERRIDE_VARS+=	NO_WFORMAT
+NO_WFORMAT.snprintf_test=
+NO_WFORMAT.sscanf_test=
+NO_WFORMAT.swprintf_test=
+NO_WFORMAT.swscanf_test=
+
 .if ${COMPILER_TYPE} == "gcc"
 # 90: use of assignment suppression and length modifier together in scanf format
-PROG_OVERRIDE_VARS+=	NO_WFORMAT
 NO_WFORMAT.scanfloat_test=
 .endif