diff --git a/sdk-go/inferable_test.go b/sdk-go/inferable_test.go
index 49754aa5..559b17eb 100644
--- a/sdk-go/inferable_test.go
+++ b/sdk-go/inferable_test.go
@@ -200,6 +200,7 @@ func TestGetSchema(t *testing.T) {
             "name": "TestFunc",
             "input": {
                 "$schema": "https://json-schema.org/draft/2020-12/schema",
+                "additionalProperties": false,
                 "type": "object",
                 "properties": {
                     "a": {"type": "integer"},
@@ -212,6 +213,7 @@ func TestGetSchema(t *testing.T) {
             "name": "TestFunc2",
             "input": {
                 "$schema": "https://json-schema.org/draft/2020-12/schema",
+                "additionalProperties": false,
                 "type": "object",
                 "properties": {
                     "c": {
diff --git a/sdk-go/service.go b/sdk-go/service.go
index b3e2d5fd..0c9cd8f7 100644
--- a/sdk-go/service.go
+++ b/sdk-go/service.go
@@ -116,7 +116,7 @@ func (s *service) RegisterFunc(fn Function) (*FunctionReference, error) {
 	}
 
 	// Get the schema for the input struct
-	reflector := jsonschema.Reflector{DoNotReference: true, Anonymous: true}
+	reflector := jsonschema.Reflector{DoNotReference: true, Anonymous: true, AllowAdditionalProperties: false}
 	schema := reflector.Reflect(reflect.New(argType).Interface())
 
 	if schema == nil {
@@ -142,7 +142,7 @@ func (s *service) RegisterFunc(fn Function) (*FunctionReference, error) {
 		return nil, fmt.Errorf("schema for function '%s' contains a $ref to an external definition. this is currently not supported. see https://go.inferable.ai/go-schema-limitation for details", fn.Name)
 	}
 
-	defs.AdditionalProperties = nil
+	defs.AdditionalProperties = jsonschema.FalseSchema
 	fn.schema = defs
 
 	s.Functions[fn.Name] = fn