diff --git a/conf/confbase.Y b/conf/confbase.Y
index 31b36173..b48a9290 100644
--- a/conf/confbase.Y
+++ b/conf/confbase.Y
@@ -56,6 +56,7 @@ CF_DECLS
 %type <a> ipa
 %type <px> prefix prefix_or_ipa
 
+%nonassoc PREFIX_DUMMY
 %nonassoc '=' '<' '>' '~' '.' GEQ LEQ NEQ
 %left '+' '-'
 %left '*' '/' '%'
diff --git a/filter/config.Y b/filter/config.Y
index a99e4a54..accf3184 100644
--- a/filter/config.Y
+++ b/filter/config.Y
@@ -211,7 +211,7 @@ pair:
  * Complex types, their bison value is struct f_val
  */
 fprefix_s:
-   IPA '/' NUM {
+   IPA '/' NUM %prec '/' {
      if (!ip_is_prefix($1, $3)) cf_error("Invalid network prefix: %I/%d", $1, $3);
      $$.type = T_PREFIX; $$.val.px.ip = $1; $$.val.px.len = $3;
    }
@@ -225,7 +225,7 @@ fprefix:
  ;
 
 fipa:
-   IPA  { $$.type = T_IP; $$.val.px.ip = $1; }
+   IPA %prec PREFIX_DUMMY { $$.type = T_IP; $$.val.px.ip = $1; }
  ;
 
 set_atom:
diff --git a/filter/test.conf b/filter/test.conf
index bce8cfec..c7fe415f 100644
--- a/filter/test.conf
+++ b/filter/test.conf
@@ -6,7 +6,7 @@
 
 router id 62.168.0.1;
 
-#define xyzzy = 120+10;
+define xyzzy = (120+10);
 
 function callme(int arg1; int arg2)
 int local1;