diff --git a/lib/filterx/expr-isset.c b/lib/filterx/expr-isset.c
index 69c18d589c..0186c382ab 100644
--- a/lib/filterx/expr-isset.c
+++ b/lib/filterx/expr-isset.c
@@ -24,7 +24,7 @@
 #include "filterx/expr-isset.h"
 #include "filterx/object-primitive.h"
 
-FilterXObject *
+static FilterXObject *
 _eval(FilterXExpr *s)
 {
   FilterXUnaryOp *self = (FilterXUnaryOp *) s;
diff --git a/lib/filterx/expr-unset.c b/lib/filterx/expr-unset.c
index 1ccee1b3f2..669656147e 100644
--- a/lib/filterx/expr-unset.c
+++ b/lib/filterx/expr-unset.c
@@ -24,7 +24,7 @@
 #include "filterx/expr-unset.h"
 #include "filterx/object-primitive.h"
 
-FilterXObject *
+static FilterXObject *
 _eval(FilterXExpr *s)
 {
   FilterXUnaryOp *self = (FilterXUnaryOp *) s;
diff --git a/lib/filterx/filterx-grammar.ym b/lib/filterx/filterx-grammar.ym
index 56c67ba5fe..c9eeab4497 100644
--- a/lib/filterx/filterx-grammar.ym
+++ b/lib/filterx/filterx-grammar.ym
@@ -49,6 +49,8 @@
 #include "filterx/filterx-config.h"
 #include "filterx/expr-function.h"
 #include "filterx/expr-condition.h"
+#include "filterx/expr-isset.h"
+#include "filterx/expr-unset.h"
 
 #include "template/templates.h"
 
@@ -84,6 +86,8 @@ construct_template_expr(LogTemplate *template)
 %token KW_TRUE, KW_FALSE
 %token KW_NULL
 %token KW_ENUM
+%token KW_ISSET
+%token KW_UNSET
 
 %type <ptr> stmts
 %type <node> stmt
@@ -156,6 +160,8 @@ expr
         | expr KW_TAV_NE expr			{ $$ = filterx_comparison_new($1, $3, FCMPX_TYPE_AND_VALUE_BASED | FCMPX_NE ); }
 	| '(' expr ')'				{ $$ = $2; }
 	| tenary				{ $$ = $1; }
+	| KW_ISSET '(' expr ')'			{ $$ = filterx_isset_new($3); }
+	| KW_UNSET '(' expr ')'			{ $$ = filterx_unset_new($3); }
 	;
 
 expr_value
diff --git a/lib/filterx/filterx-parser.c b/lib/filterx/filterx-parser.c
index 1baa95a7b7..242978ae95 100644
--- a/lib/filterx/filterx-parser.c
+++ b/lib/filterx/filterx-parser.c
@@ -48,6 +48,9 @@ static CfgLexerKeyword filterx_keywords[] =
   { "else",               KW_ELSE },
   { "elif",               KW_ELIF },
 
+  { "isset",              KW_ISSET },
+  { "unset",              KW_UNSET },
+
   { CFG_KEYWORD_STOP },
 };