diff --git a/qutebrowser/config/configtypes.py b/qutebrowser/config/configtypes.py
index 6dd3fa7e4..953012acd 100644
--- a/qutebrowser/config/configtypes.py
+++ b/qutebrowser/config/configtypes.py
@@ -546,7 +546,8 @@ class Command(BaseType):
         self._basic_validation(value)
         if not value:
             return
-        elif value.split()[0] not in cmdutils.cmd_dict:
+        splitted = value.split()
+        if not splitted or  splitted[0] not in cmdutils.cmd_dict:
             raise configexc.ValidationError(value, "must be a valid command!")
 
     def complete(self):
diff --git a/tests/config/test_configtypes.py b/tests/config/test_configtypes.py
index 5a38115f2..966c13083 100644
--- a/tests/config/test_configtypes.py
+++ b/tests/config/test_configtypes.py
@@ -706,7 +706,7 @@ class TestCommand:
     def test_validate_valid(self, klass, val):
         klass(none_ok=True).validate(val)
 
-    @pytest.mark.parametrize('val', ['', 'cmd3', 'cmd3  foo bar'])
+    @pytest.mark.parametrize('val', ['', 'cmd3', 'cmd3  foo bar', ' '])
     def test_validate_invalid(self, klass, val):
         with pytest.raises(configexc.ValidationError):
             klass().validate(val)