diff --git a/src/lua_mathlib.c b/src/lua_mathlib.c
index 8ca2e17af..f4b5ca5fe 100644
--- a/src/lua_mathlib.c
+++ b/src/lua_mathlib.c
@@ -77,7 +77,9 @@ static int lib_finecosine(lua_State *L)
 
 static int lib_finetangent(lua_State *L)
 {
-	lua_pushfixed(L, FINETANGENT((luaL_checkangle(L, 1)>>ANGLETOFINESHIFT) & FINEMASK));
+	// HACK: add ANGLE_90 to make tan() in Lua start at 0 like it should
+	// use & 4095 instead of & FINEMASK (8191), so it doesn't go out of the array's bounds
+	lua_pushfixed(L, FINETANGENT(((luaL_checkangle(L, 1)+ANGLE_90)>>ANGLETOFINESHIFT) & 4095));
 	return 1;
 }