diff --git a/src/Functions/FunctionsComparison.h b/src/Functions/FunctionsComparison.h
index 0a3d544f9e5ff6e04db90308f266c6b98559a888..436502aead4cee031c3912bb589723e4d0f34ea1 100644
--- a/src/Functions/FunctionsComparison.h
+++ b/src/Functions/FunctionsComparison.h
@@ -1213,7 +1213,7 @@ public:
         const bool left_is_string = isStringOrFixedString(which_left);
         const bool right_is_string = isStringOrFixedString(which_right);
 
-        bool date_and_datetime = (left_type != right_type) &&
+        bool date_and_datetime = (which_left.idx != which_right.idx) &&
             which_left.isDateOrDateTime() && which_right.isDateOrDateTime();
 
         if (left_is_num && right_is_num && !date_and_datetime)
diff --git a/tests/performance/datetime_comparison.xml b/tests/performance/datetime_comparison.xml
new file mode 100644
index 0000000000000000000000000000000000000000..2d47ded0b1a0ebef72d46b426862ddd90635b187
--- /dev/null
+++ b/tests/performance/datetime_comparison.xml
@@ -0,0 +1,5 @@
+<test>
+    <query>SELECT count() FROM numbers(1000000000) WHERE materialize(now()) > toString(toDateTime('2020-09-30 00:00:00'))</query>
+    <query>SELECT count() FROM numbers(1000000000) WHERE materialize(now()) > toUInt32(toDateTime('2020-09-30 00:00:00'))</query>
+    <query>SELECT count() FROM numbers(1000000000) WHERE materialize(now()) > toDateTime('2020-09-30 00:00:00')</query>
+</test>