diff --git a/configure b/configure
index 59dd4532df..6125bcbc32 100755
--- a/configure
+++ b/configure
@@ -3657,6 +3657,9 @@ probe_libc(){
     elif check_${pfx}cpp_condition sys/brand.h "defined LABELED_BRAND_NAME"; then
         eval ${pfx}libc_type=solaris
         add_${pfx}cppflags -D__EXTENSIONS__ -D_XOPEN_SOURCE=600
+    else
+        eval ${pfx}libc_type=unknown
+        add_${pfx}cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
     fi
 }