diff --git a/trytond/trytond/model/fields/char.py b/trytond/trytond/model/fields/char.py
index 1d113d9fcf0..7b0805c2f83 100644
--- a/trytond/trytond/model/fields/char.py
+++ b/trytond/trytond/model/fields/char.py
@@ -149,7 +149,7 @@ def convert_domain(self, domain, tables, Model):
             threshold = context.get(
                 '%s.%s.search_similarity' % (Model.__name__, name),
                 context.get('search_similarity'))
-            if database.has_similarity() and is_full_text(value) and threshold:
+            if threshold and database.has_similarity() and is_full_text(value):
                 sim_value = unescape_wildcard(value)
                 sim_value = self._domain_value(operator, sim_value)
                 expression = (
diff --git a/trytond/trytond/tools/misc.py b/trytond/trytond/tools/misc.py
index 79900f058af..26fdc32ca32 100644
--- a/trytond/trytond/tools/misc.py
+++ b/trytond/trytond/tools/misc.py
@@ -245,6 +245,8 @@ def unescape_wildcard(string, wildcards='%_', escape='\\'):
 
 
 def is_full_text(value, escape='\\'):
+    if not value:
+        return False
     escaped = strip_wildcard(value, escape=escape)
     escaped = escaped.replace(escape + '%', '').replace(escape + '_', '')
     if '%' in escaped or '_' in escaped: