diff --git a/Cargo.toml b/Cargo.toml
index c386fd3..a3f4b83 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "rlua"
-version = "0.13.1-alpha.0"
+version = "0.14.0-alpha.0"
 authors = ["kyren <catherine@chucklefish.org>"]
 description = "High level bindings to Lua 5.3"
 repository = "https://github.com/chucklefish/rlua"
diff --git a/src/lua.rs b/src/lua.rs
index 14b0455..c858ef3 100644
--- a/src/lua.rs
+++ b/src/lua.rs
@@ -46,14 +46,22 @@ unsafe impl Send for Lua {}
 impl Drop for Lua {
     fn drop(&mut self) {
         unsafe {
-            if !self.ephemeral {
-                let top = ffi::lua_gettop(self.state);
-                rlua_assert!(
-                    top == REF_STACK_SIZE,
-                    "stack problem detected, stack top is {}",
-                    top - REF_STACK_SIZE
-                );
+            if cfg!(debug_assertions) {
+                for use_count in &self.ref_stack_slots {
+                    rlua_assert!(use_count.get() == 0, "live stack reference detected");
+                }
 
+                if !self.ephemeral {
+                    let top = ffi::lua_gettop(self.state);
+                    rlua_assert!(
+                        top == REF_STACK_SIZE,
+                        "stack problem detected, stack top is {}",
+                        top - REF_STACK_SIZE
+                    );
+                }
+            }
+
+            if !self.ephemeral {
                 let extra_data = *(ffi::lua_getextraspace(self.state) as *mut *mut ExtraData);
                 *(*extra_data).registry_unref_list.lock().unwrap() = None;
                 Box::from_raw(extra_data);
@@ -819,7 +827,7 @@ impl Lua {
                 RefType::Stack { stack_slot } => {
                     let ref_slot = &self.ref_stack_slots[(stack_slot - 1) as usize];
                     let ref_count = ref_slot.get();
-                    rlua_assert!(ref_count > 0, "ref slot use count has gone below zero");
+                    rlua_debug_assert!(ref_count > 0, "ref slot use count has gone below zero");
                     ref_slot.set(ref_count - 1);
                     if ref_count == 1 {
                         ffi::lua_pushnil(self.state);
@@ -1125,7 +1133,7 @@ impl Lua {
         }));
         *(ffi::lua_getextraspace(state) as *mut *mut ExtraData) = extra_data;
 
-        rlua_assert!(ffi::lua_gettop(state) == 0, "stack leak during creation");
+        rlua_debug_assert!(ffi::lua_gettop(state) == 0, "stack leak during creation");
         check_stack(state, REF_STACK_SIZE);
         ffi::lua_settop(state, REF_STACK_SIZE);
 
diff --git a/src/macros.rs b/src/macros.rs
index fb10a07..233495f 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -40,6 +40,16 @@ macro_rules! rlua_assert {
     };
 }
 
+macro_rules! rlua_debug_assert {
+    ($cond:expr, $msg:expr) => {
+        debug_assert!($cond, concat!("rlua internal error: ", $msg));
+    };
+
+    ($cond:expr, $msg:expr, $($arg:tt)+) => {
+        debug_assert!($cond, concat!("rlua internal error: ", $msg), $($arg)+);
+    };
+}
+
 macro_rules! rlua_abort {
     ($msg:expr) => {
         {
diff --git a/src/string.rs b/src/string.rs
index 1610f3e..835eb54 100644
--- a/src/string.rs
+++ b/src/string.rs
@@ -73,7 +73,7 @@ impl<'lua> String<'lua> {
             check_stack(lua.state, 1);
 
             lua.push_ref(&self.0);
-            rlua_assert!(
+            rlua_debug_assert!(
                 ffi::lua_type(lua.state, -1) == ffi::LUA_TSTRING,
                 "string ref is not string type"
             );
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
index f24506f..e40f102 100644
--- a/src/tests/mod.rs
+++ b/src/tests/mod.rs
@@ -781,9 +781,9 @@ fn large_args() {
     );
 }
 
+#[test]
 fn large_args_ref() {
     let lua = Lua::new();
-    let globals = lua.globals();
 
     let f = lua.create_function(|_, args: Variadic<String>| {
         for i in 0..args.len() {
diff --git a/src/tests/thread.rs b/src/tests/thread.rs
index 56b671d..48284d7 100644
--- a/src/tests/thread.rs
+++ b/src/tests/thread.rs
@@ -100,7 +100,7 @@ fn coroutine_panic() {
     match catch_unwind(|| -> Result<()> {
         // check that coroutines propagate panics correctly
         let lua = Lua::new();
-        let thrd_main = lua.create_function(|lua, ()| -> Result<()> {
+        let thrd_main = lua.create_function(|_, ()| -> Result<()> {
             panic!("test_panic");
         })?;
         lua.globals().set("main", thrd_main.clone())?;
diff --git a/src/userdata.rs b/src/userdata.rs
index be8fb32..914914c 100644
--- a/src/userdata.rs
+++ b/src/userdata.rs
@@ -420,7 +420,7 @@ impl<'lua> AnyUserData<'lua> {
 
             lua.push_ref(&self.0);
 
-            rlua_assert!(
+            rlua_debug_assert!(
                 ffi::lua_getmetatable(lua.state, -1) != 0,
                 "AnyUserData missing metatable"
             );
diff --git a/src/util.rs b/src/util.rs
index b5ba46a..99b623c 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -158,7 +158,7 @@ where
 //   3) Otherwise, interprets the error as the appropriate lua error.
 // Uses 2 stack spaces, does not call lua_checkstack.
 pub unsafe fn pop_error(state: *mut ffi::lua_State, err_code: c_int) -> Error {
-    rlua_assert!(
+    rlua_debug_assert!(
         err_code != ffi::LUA_OK && err_code != ffi::LUA_YIELD,
         "pop_error called with non-error return code"
     );
@@ -229,7 +229,7 @@ pub unsafe fn push_userdata<T>(state: *mut ffi::lua_State, t: T) -> Result<()> {
 
 pub unsafe fn get_userdata<T>(state: *mut ffi::lua_State, index: c_int) -> *mut T {
     let ud = ffi::lua_touserdata(state, index) as *mut T;
-    rlua_assert!(!ud.is_null(), "userdata pointer is null");
+    rlua_debug_assert!(!ud.is_null(), "userdata pointer is null");
     ud
 }
 
@@ -243,7 +243,7 @@ pub unsafe fn take_userdata<T>(state: *mut ffi::lua_State) -> T {
     get_destructed_userdata_metatable(state);
     ffi::lua_setmetatable(state, -2);
     let ud = ffi::lua_touserdata(state, -1) as *mut T;
-    rlua_assert!(!ud.is_null(), "userdata pointer is null");
+    rlua_debug_assert!(!ud.is_null(), "userdata pointer is null");
     ffi::lua_pop(state, 1);
     ptr::read(ud)
 }