diff --git a/configure b/configure
index 5cf1ef6515fb46a661f5e738f1e3930de496d10f..617ad557a95d73cfe47c5ffe3eb05bf3150346ed 100755
--- a/configure
+++ b/configure
@@ -362,7 +362,7 @@ disabled_any(){
 
 set_default(){
     for opt; do
-        eval test -z "\$$opt" && eval $opt=\$${opt}_default
+        eval : \${$opt:=\$${opt}_default}
     done
 }