diff --git a/.golangci.yml b/.golangci.yml
index e3400d6..7886c7c 100644
--- a/.golangci.yml
+++ b/.golangci.yml
@@ -10,6 +10,7 @@ linters:
   enable:
     - errcheck
     - errname
+    - gochecksumtype
     - govet
     - ineffassign
     - revive
diff --git a/internal/schema/ast/ast.go b/internal/schema/ast/ast.go
index d01359a..e435cb0 100644
--- a/internal/schema/ast/ast.go
+++ b/internal/schema/ast/ast.go
@@ -42,7 +42,8 @@ import (
 
 // The human readable format is not 1-1 convertible with JSON. The JSON format
 // is lossy. It loses formatting, such as comments, ordering of fields, etc...
-
+//
+//sumtype:decl
 type Node interface {
 	isNode()
 	// Pos returns first token of the node
@@ -97,6 +98,7 @@ func (s *Schema) End() token.Position {
 	return token.Position{}
 }
 
+//sumtype:decl
 type Declaration interface {
 	Node
 	isDecl()
@@ -165,6 +167,8 @@ func (t *CommonTypeDecl) End() token.Position {
 // 1. A record type
 // 2. A set type (Set<String>)
 // 3. A path (Namespace::EntityType or String)
+//
+//sumtype:decl
 type Type interface {
 	Node
 	isType()
@@ -377,6 +381,8 @@ func (r *Ref) End() token.Position {
 }
 
 // Name is an IDENT or STR
+//
+//sumtype:decl
 type Name interface {
 	Node
 	isName()
diff --git a/internal/schema/ast/ast_test.go b/internal/schema/ast/ast_test.go
index 3792dfc..2f1f7fa 100644
--- a/internal/schema/ast/ast_test.go
+++ b/internal/schema/ast/ast_test.go
@@ -116,32 +116,6 @@ func Test_formatter_printInd_panic(t *testing.T) {
 	p.printInd("test")
 }
 
-type unknownNode struct {
-	Node // Embed Node interface to satisfy type checker
-}
-
-func Test_formatter_print_panic(t *testing.T) {
-	p := &formatter{
-		w: &bytes.Buffer{},
-	}
-
-	defer func() {
-		r := recover()
-		if r == nil {
-			t.Fatal("expected panic, got none")
-		}
-		msg, ok := r.(string)
-		if !ok {
-			t.Fatalf("expected string panic, got %T", r)
-		}
-		if !strings.Contains(msg, "unhandled node type") {
-			t.Errorf("expected panic message about unhandled type, got %q", msg)
-		}
-	}()
-
-	p.print(unknownNode{})
-}
-
 func Test_printBracketList_panic(t *testing.T) {
 	p := &formatter{
 		w: &bytes.Buffer{},
@@ -164,26 +138,3 @@ func Test_printBracketList_panic(t *testing.T) {
 	var emptyList []Node
 	printBracketList(p, emptyList, false)
 }
-
-type unknownType struct {
-	Type // Embed Type interface to satisfy it
-}
-
-func TestConvertType_Panic(t *testing.T) {
-	defer func() {
-		r := recover()
-		if r == nil {
-			t.Fatal("expected panic, got none")
-		}
-		msg, ok := r.(string)
-		if !ok {
-			t.Fatalf("expected string panic, got %T", r)
-		}
-		expected := "unknownType is not an AST type"
-		if !strings.Contains(msg, expected) {
-			t.Errorf("expected panic message to contain %q, got %q", expected, msg)
-		}
-	}()
-
-	convertType(unknownType{})
-}
diff --git a/internal/schema/ast/convert_human.go b/internal/schema/ast/convert_human.go
index 5ade4e8..4586ce1 100644
--- a/internal/schema/ast/convert_human.go
+++ b/internal/schema/ast/convert_human.go
@@ -104,6 +104,10 @@ func convertNamespace(n *Namespace) *JSONNamespace {
 				commonType.Annotations[a.Key.String()] = a.Value.String()
 			}
 			jsNamespace.CommonTypes[astDecl.Name.String()] = commonType
+		case *CommentBlock:
+			// comment blocks intentionally dropped.
+		case *Namespace:
+			// namespaces intentionally not handled.
 		}
 	}
 	return jsNamespace
diff --git a/internal/schema/ast/convert_json.go b/internal/schema/ast/convert_json.go
index c0f353e..86f69d1 100644
--- a/internal/schema/ast/convert_json.go
+++ b/internal/schema/ast/convert_json.go
@@ -192,6 +192,8 @@ func convertJSONAppliesTo(appliesTo *JSONAppliesTo) *AppliesTo {
 			at.ContextRecord = t
 		case *Path:
 			at.ContextPath = t
+		case *SetType:
+			panic("SetType not yet handled in convertJSONAppliesTo")
 		}
 	}