diff --git a/conf/confbase.Y b/conf/confbase.Y
index c6143012..4626d440 100644
--- a/conf/confbase.Y
+++ b/conf/confbase.Y
@@ -53,7 +53,7 @@ CF_DECLS
 
 %type <i> expr bool pxlen
 %type <time> datetime
-%type <px> prefix
+%type <px> prefix prefix_or_ipa
 
 %nonassoc '=' '<' '>' '~' '.' GEQ LEQ NEQ
 %left '+' '-'
@@ -118,6 +118,11 @@ prefix:
    }
  ;
 
+prefix_or_ipa:
+   prefix
+ | IPA { $$.addr = $1; $$.len = BITS_PER_IP_ADDRESS; }
+ ;
+
 pxlen:
    '/' NUM {
      if ($2 < 0 || $2 > BITS_PER_IP_ADDRESS) cf_error("Invalid prefix length %d", $2);