diff --git a/src/ffi/internals51.rs b/src/ffi/internals51.rs
new file mode 100644
index 0000000..24751e2
--- /dev/null
+++ b/src/ffi/internals51.rs
@@ -0,0 +1,120 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2020 A. Orlenko
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+use std::os::raw::*;
+
+use crate::ffi::{lua_Alloc, lua_CFunction, lua_Hook, lua_Number, lua_State};
+
+#[repr(C)]
+struct lua_StateExt {
+    next: *mut c_void,
+    tt: u8,
+    marked: u8,
+    status: u8,
+    top: *mut c_void,
+    base: *mut c_void,
+    l_G: *mut global_State,
+    ci: *mut c_void,
+    savedpc: *const c_void,
+    stack_last: *mut c_void,
+    stack: *mut c_void,
+    end_ci: *mut c_void,
+    base_ci: *mut c_void,
+    stacksize: c_int,
+    size_ci: c_int,
+    nCcalls: c_ushort,
+    baseCcalls: c_ushort,
+    hookmask: u8,
+    allowhook: u8,
+    basehookcount: c_int,
+    hookcount: c_int,
+    hook: Option<lua_Hook>,
+    l_gt: TValue,
+    env: TValue,
+    openupval: *mut c_void,
+    gclist: *mut c_void,
+    errorJmp: *mut c_void,
+    errfunc: isize,
+}
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+struct TValue {
+    value: Value,
+    tt: c_int,
+}
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+union Value {
+    gc: *mut c_void,
+    p: *mut c_void,
+    n: lua_Number,
+    b: c_int,
+}
+
+#[repr(C)]
+struct global_State {
+    strt: stringtable,
+    frealloc: Option<lua_Alloc>,
+    ud: *mut c_void,
+    currentwhite: u8,
+    gcstate: u8,
+    sweepstrgc: c_int,
+    rootgc: *mut c_void,
+    sweepgc: *mut c_void,
+    gray: *mut c_void,
+    grayagain: *mut c_void,
+    weak: *mut c_void,
+    tmudata: *mut c_void,
+    buff: Mbuffer,
+    GCthreshold: usize,
+    totalbytes: usize,
+    estimate: usize,
+    gcdept: usize,
+    gcpause: c_int,
+    gcstepmul: c_int,
+    panic: Option<lua_CFunction>,
+    l_registry: TValue,
+    mainthread: *mut lua_State,
+    // Other fields ommited
+}
+
+#[repr(C)]
+struct stringtable {
+    hash: *mut c_void,
+    nuse: c_uint,
+    size: c_int,
+}
+
+#[repr(C)]
+struct Mbuffer {
+    buffer: *mut c_char,
+    n: usize,
+    buffsize: usize,
+}
+
+pub unsafe fn lua_getmainstate(state: *mut lua_State) -> *mut lua_State {
+    let state = state as *mut lua_StateExt;
+    let global = (*state).l_G;
+    (*global).mainthread
+}
diff --git a/src/ffi/mod.rs b/src/ffi/mod.rs
index 78059a2..cab2f09 100644
--- a/src/ffi/mod.rs
+++ b/src/ffi/mod.rs
@@ -170,6 +170,9 @@ pub use self::lua::{lua_isyieldable, lua_version};
 #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
 pub use self::lua::{lua_callk, lua_pcallk, lua_upvalueid, lua_upvaluejoin, lua_yieldk};
 
+#[cfg(feature = "lua51")]
+pub use self::internals51::lua_getmainstate;
+
 // auxiliary library types
 pub use self::lauxlib::luaL_Reg;
 
@@ -284,6 +287,9 @@ mod glue {
 #[cfg(any(feature = "lua52", feature = "lua51", feature = "luajit"))]
 mod compat53;
 
+#[cfg(feature = "lua51")]
+mod internals51;
+
 mod lauxlib;
 mod lua;
 mod luaconf;
diff --git a/src/lua.rs b/src/lua.rs
index e13dcb5..b444384 100644
--- a/src/lua.rs
+++ b/src/lua.rs
@@ -279,7 +279,7 @@ impl Lua {
     #[allow(clippy::missing_safety_doc)]
     pub unsafe fn init_from_ptr(state: *mut ffi::lua_State) -> Lua {
         let main_state = get_main_state(state);
-        let main_state_top = ffi::lua_gettop(state);
+        let main_state_top = ffi::lua_gettop(main_state);
 
         let ref_thread = mlua_expect!(
             protect_lua_closure(main_state, 0, 0, |state| {
@@ -324,7 +324,7 @@ impl Lua {
         }));
 
         mlua_expect!(
-            push_gc_userdata(state, Arc::downgrade(&extra)),
+            push_gc_userdata(main_state, Arc::downgrade(&extra)),
             "Error while storing extra data",
         );
         mlua_expect!(
diff --git a/src/util.rs b/src/util.rs
index eba93e9..d729155 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -493,7 +493,19 @@ pub unsafe fn get_main_state(state: *mut ffi::lua_State) -> *mut ffi::lua_State
         ffi::lua_pop(state, 1);
         main_state
     }
-    #[cfg(any(feature = "lua51", feature = "luajit"))]
+    #[cfg(feature = "lua51")]
+    {
+        // Check the current state first
+        let is_main_state = ffi::lua_pushthread(state) == 1;
+        ffi::lua_pop(state, 1);
+        if is_main_state {
+            state
+        } else {
+            // The function below is a dirty hack and uses Lua private internals
+            ffi::lua_getmainstate(state)
+        }
+    }
+    #[cfg(feature = "luajit")]
     state
 }