diff --git a/res/modules/internal/maths_inline.lua b/res/modules/internal/maths_inline.lua
index 36c0aecfe..ecb77df97 100644
--- a/res/modules/internal/maths_inline.lua
+++ b/res/modules/internal/maths_inline.lua
@@ -238,3 +238,17 @@ function vec2.mix(a, b, t, dest)
         }
     end
 end
+
+function mat4.idt(dst)
+    if dst then
+        for i=1,16 do
+            dst[i] = (i % 5 == 1) and 1 or 0
+        end
+    end
+    return {
+        1, 0, 0, 0,
+        0, 1, 0, 0,
+        0, 0, 1, 0,
+        0, 0, 0, 1
+    }
+end