diff --git a/ovn/lib/expr.c b/ovn/lib/expr.c
index b50475245a4..8cfdf34fa6a 100644
--- a/ovn/lib/expr.c
+++ b/ovn/lib/expr.c
@@ -581,6 +581,11 @@ make_cmp(struct expr_context *ctx,
                         f->symbol->name);
             goto exit;
         }
+        if (!cs->n_values) {
+            lexer_error(ctx->lexer, "Only == and != operators may be used "
+                        "to compare a field against an empty value set.");
+            goto exit;
+        }
         if (cs->values[0].masked) {
             lexer_error(ctx->lexer, "Only == and != operators may be used "
                         "with masked constants.  Consider using subfields "
diff --git a/tests/ovn.at b/tests/ovn.at
index 886981d5183..71518d97db4 100644
--- a/tests/ovn.at
+++ b/tests/ovn.at
@@ -355,6 +355,8 @@ ip4.src == {1.2.3.4, $set1, $unknownset} => Syntax error at `$unknownset' expect
 eth.src == {$set3, badmac, 00:00:00:00:00:01} => Syntax error at `badmac' expecting constant.
 
 ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((())))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) => Parentheses nested too deeply.
+
+ct_label > $set4 => Only == and != operators may be used to compare a field against an empty value set.
 ]])
 sed 's/ =>.*//' test-cases.txt > input.txt
 sed 's/.* => //' test-cases.txt > expout