diff --git a/maxscale-system-test/masking_auto_firewall.cpp b/maxscale-system-test/masking_auto_firewall.cpp
index fcbb50bfa..f8672211d 100644
--- a/maxscale-system-test/masking_auto_firewall.cpp
+++ b/maxscale-system-test/masking_auto_firewall.cpp
@@ -87,6 +87,9 @@ void run(TestConnections& test)
     // This should NOT go through as a function is used with a masked column (that happens to be uppercase).
     test_one(test, "SELECT LENGTH(A), b FROM masking_auto_firewall", Expect::FAILURE);
 
+    // This should NOT go through as a function is used with a masked column.
+    test_one(test, "SELECT CAST(A as CHAR), b FROM masking_auto_firewall", Expect::FAILURE);
+
     // This SHOULD go through as a function is NOT used with a masked column
     // in a prepared statement.
     test_one(test, "PREPARE ps1 FROM 'SELECT a, LENGTH(b) FROM masking_auto_firewall'", Expect::SUCCESS);
@@ -118,6 +121,9 @@ void run(TestConnections& test)
     // This should NOT succeed as a masked column is used in the statment.
     test_one(test, "select 1 UNION select a FROM masking_auto_firewall", Expect::FAILURE);
 
+    // This should NOT succeed as a masked column is used in the statment.
+    test_one(test, "select 1 UNION ALL select a FROM masking_auto_firewall", Expect::FAILURE);
+
     // This should NOT succeed as '*' is used in the statment.
     test_one(test, "select 1 UNION select * FROM masking_auto_firewall", Expect::FAILURE);
 
diff --git a/query_classifier/qc_sqlite/qc_sqlite.cc b/query_classifier/qc_sqlite/qc_sqlite.cc
index b5364732c..a1f256694 100644
--- a/query_classifier/qc_sqlite/qc_sqlite.cc
+++ b/query_classifier/qc_sqlite/qc_sqlite.cc
@@ -928,6 +928,7 @@ public:
             case TK_BITAND:
             case TK_BITOR:
             case TK_CASE:
+            case TK_CAST:
             case TK_IN:
             case TK_ISNULL:
             case TK_MINUS:
@@ -1258,6 +1259,11 @@ public:
         IGNORE_COMPOUND_SELECTS
     };
 
+    bool is_significant_union(const Select* pSelect)
+    {
+        return ((pSelect->op == TK_UNION) || (pSelect->op == TK_ALL)) && pSelect->pPrior;
+    }
+
     void update_field_infos_from_select(QcAliases& aliases,
                                         uint32_t context,
                                         const Select* pSelect,
@@ -1357,7 +1363,7 @@ public:
 
         if (compound_approach == ANALYZE_COMPOUND_SELECTS)
         {
-            if (((pSelect->op == TK_UNION) || (pSelect->op == TK_ALL)) && pSelect->pPrior)
+            if (is_significant_union(pSelect))
             {
                 const Select* pPrior = pSelect->pPrior;
 
@@ -2139,7 +2145,7 @@ public:
         }
 
         QcAliases aliases;
-        uint32_t context = (pSelect->op == TK_UNION && pSelect->pPrior) ? QC_FIELD_UNION : 0;
+        uint32_t context = is_significant_union(pSelect) ? QC_FIELD_UNION : 0;
         update_field_infos_from_select(aliases, context, pSelect, NULL);
     }
 
@@ -4002,6 +4008,9 @@ static const char* get_token_symbol(int token)
     case TK_CASE:
         return "case";
 
+    case TK_CAST:
+        return "cast";
+
     case TK_IN:
         return "in";