diff --git a/lapi.c b/lapi.c
index 98d23665..4f4e3021 100644
--- a/lapi.c
+++ b/lapi.c
@@ -1199,7 +1199,7 @@ LUA_API int lua_gc (lua_State *L, int what, ...) {
     }
     case LUA_GCSTEP: {
       lu_byte oldstp = g->gcstp;
-      l_obj n = va_arg(argp, int);
+      l_obj n = cast(l_obj, va_arg(argp, size_t));
       int work = 0;  /* true if GC did some work */
       g->gcstp = 0;  /* allow GC to run (other bits must be zero here) */
       if (n <= 0)
diff --git a/lbaselib.c b/lbaselib.c
index a7b6c3ed..b296c4b7 100644
--- a/lbaselib.c
+++ b/lbaselib.c
@@ -216,7 +216,7 @@ static int luaB_collectgarbage (lua_State *L) {
     }
     case LUA_GCSTEP: {
       lua_Integer n = luaL_optinteger(L, 2, 0);
-      int res = lua_gc(L, o, (int)n);
+      int res = lua_gc(L, o, cast_sizet(n));
       checkvalres(res);
       lua_pushboolean(L, res);
       return 1;
diff --git a/manual/manual.of b/manual/manual.of
index 93e3a114..f0a2ed94 100644
--- a/manual/manual.of
+++ b/manual/manual.of
@@ -3326,7 +3326,7 @@ Returns the remainder of dividing the current amount of bytes of
 memory in use by Lua by 1024.
 }
 
-@item{@defid{LUA_GCSTEP} (int n)|
+@item{@defid{LUA_GCSTEP} (size_t n)|
 Performs a step of garbage collection.
 }