diff --git a/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/TypeComputeUtils.java b/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/TypeComputeUtils.java
index 448ab4c..f1f1be3 100644
--- a/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/TypeComputeUtils.java
+++ b/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/TypeComputeUtils.java
@@ -168,8 +168,9 @@
         }
         IAType resultType = type;
         if ((category & NULLABLE) != 0 || (category & NULL) != 0) {
-            resultType = AUnionType.createUnknownableType(resultType);
-        } else if ((category & MISSABLE) != 0 || (category & MISSING) != 0) {
+            resultType = AUnionType.createNullableType(resultType);
+        }
+        if ((category & MISSABLE) != 0 || (category & MISSING) != 0) {
             resultType = AUnionType.createMissableType(resultType);
         }
         return resultType;