diff --git a/src/Expr.cc b/src/Expr.cc
index 18deec804c..9f333c641e 100644
--- a/src/Expr.cc
+++ b/src/Expr.cc
@@ -2383,11 +2383,10 @@ IndexExpr::IndexExpr(ExprPtr arg_op1, ListExprPtr arg_op2, bool arg_is_slice, bo
         return;
 
     if ( op1->GetType()->Tag() == TYPE_TABLE ) { // Check for a table[pattern] being indexed by a string
-        auto table_type = op1->GetType()->AsTableType();
-        auto& it = table_type->GetIndexTypes();
-        auto& rhs_type = op2->GetType()->AsTypeList()->GetTypes();
-        if ( it.size() == 1 && it[0]->Tag() == TYPE_PATTERN && table_type->Yield() && rhs_type.size() == 1 &&
-             rhs_type[0]->Tag() == TYPE_STRING ) {
+        const auto& table_type = op1->GetType()->AsTableType();
+        const auto& rhs_type = op2->GetType()->AsTypeList()->GetTypes();
+        if ( table_type->IsPatternIndex() && table_type->Yield() && rhs_type.size() == 1 &&
+             IsString(rhs_type[0]->Tag()) ) {
             is_pattern_table = true;
             SetType(make_intrusive<VectorType>(op1->GetType()->Yield()));
             return;
diff --git a/src/Type.cc b/src/Type.cc
index 4fd9fa9f52..a9da69e760 100644
--- a/src/Type.cc
+++ b/src/Type.cc
@@ -389,6 +389,13 @@ bool IndexType::IsSubNetIndex() const {
     return false;
 }
 
+bool IndexType::IsPatternIndex() const {
+    const auto& types = indices->GetTypes();
+    if ( types.size() == 1 && types[0]->Tag() == TYPE_PATTERN )
+        return true;
+    return false;
+}
+
 detail::TraversalCode IndexType::Traverse(detail::TraversalCallback* cb) const {
     auto tc = cb->PreType(this);
     HANDLE_TC_TYPE_PRE(tc);
diff --git a/src/Type.h b/src/Type.h
index 6b69eb8e37..142fe2d331 100644
--- a/src/Type.h
+++ b/src/Type.h
@@ -356,6 +356,9 @@ public:
     // Returns true if this table is solely indexed by subnet.
     bool IsSubNetIndex() const;
 
+    // Returns true if this table has a single index of type pattern.
+    bool IsPatternIndex() const;
+
     detail::TraversalCode Traverse(detail::TraversalCallback* cb) const override;
 
 protected:
diff --git a/src/Val.cc b/src/Val.cc
index d861d69386..a8f6f0d2e2 100644
--- a/src/Val.cc
+++ b/src/Val.cc
@@ -1547,8 +1547,7 @@ void TableVal::Init(TableTypePtr t, bool ordered) {
     else
         subnets = nullptr;
 
-    auto& it = table_type->GetIndexTypes();
-    if ( it.size() == 1 && it[0]->Tag() == TYPE_PATTERN && table_type->Yield() )
+    if ( table_type->IsPatternIndex() && table_type->Yield() )
         pattern_matcher = new TablePatternMatcher(this, table_type->Yield());
 
     table_hash = new detail::CompositeHash(table_type->GetIndices());
diff --git a/src/script_opt/CPP/Exprs.cc b/src/script_opt/CPP/Exprs.cc
index afef3ce3cd..f798b4f91c 100644
--- a/src/script_opt/CPP/Exprs.cc
+++ b/src/script_opt/CPP/Exprs.cc
@@ -391,8 +391,7 @@ string CPPCompile::GenIndexExpr(const Expr* e, GenType gt) {
         auto ind_expr = e->GetOp2()->AsListExpr()->Exprs()[0];
         auto is_pat_str_ind = false;
 
-        auto& indices = aggr_t->AsTableType()->GetIndices()->GetTypes();
-        if ( indices.size() == 1 && indices[0]->Tag() == TYPE_PATTERN && ind_expr->GetType()->Tag() == TYPE_STRING )
+        if ( aggr_t->AsTableType()->IsPatternIndex() && ind_expr->GetType()->Tag() == TYPE_STRING )
             is_pat_str_ind = true;
 
         if ( inside_when ) {