Invalid #include directive

Hello, everyone!

I’m struggling with a very simple task, and I surprisingly can’t google it out. I’m willing to include a .cginc file into my custom surface shader, and the same cginc works perfectly in a vert/frag shader, but in the surf one gives a “Invalid #include directive” error. What I might’ve missed? Should I add something to the cginc for it to work with surface shaders?

Edit: in the comments I added a sample shader code, which is the standard unity shader that is created when you, well, create one with the include directive that doesn’t work. I’m using Unity 2017.2.1f if that’s relevant.

Shader "Custom/Standard" {
     Properties {
         _Color ("Color", Color) = (1,1,1,1)
         _MainTex ("Albedo (RGB)", 2D) = "white" {}
         _Glossiness ("Smoothness", Range(0,1)) = 0.5
         _Metallic ("Metallic", Range(0,1)) = 0.0
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         
         CGPROGRAM
         #pragma surface surf Standard fullforwardshadows
         #include "Assets\Resources\Shaders\UnlitLightmap.cginc"
         #pragma target 3.0
 
         sampler2D _MainTex;
 
         struct Input {
             float2 uv_MainTex;
         };
 
         half _Glossiness;
         half _Metallic;
         fixed4 _Color;
 
         void surf (Input IN, inout SurfaceOutputStandard o) {
             fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
             o.Albedo = c.rgb;
             o.Metallic = _Metallic;
             o.Smoothness = _Glossiness;
             o.Alpha = c.a;
         }
         ENDCG
     }
     FallBack "Diffuse"
 }

Try with a relative path, not absolute, and with forward slashes