diff --git a/src/module.rs b/src/module.rs
index bbce6de..e5ad87d 100644
--- a/src/module.rs
+++ b/src/module.rs
@@ -39,6 +39,9 @@ use {Error, MemoryInstance, Module, RuntimeValue, Signature, TableInstance};
 #[derive(Clone, Debug)]
 pub struct ModuleRef(pub(crate) Rc<ModuleInstance>);
 
+unsafe impl Sync for ModuleRef {}
+unsafe impl Send for ModuleRef {}
+
 impl ::core::ops::Deref for ModuleRef {
     type Target = ModuleInstance;
     fn deref(&self) -> &ModuleInstance {
@@ -164,6 +167,9 @@ pub struct ModuleInstance {
     exports: RefCell<HashMap<String, ExternVal>>,
 }
 
+unsafe impl Sync for ModuleInstance {}
+unsafe impl Send for ModuleInstance {}
+
 impl ModuleInstance {
     fn default() -> Self {
         ModuleInstance {