diff --git a/shader.md b/shader.md
index 136d65d..151efa7 100644
--- a/shader.md
+++ b/shader.md
@@ -157,6 +157,7 @@ Depending on the shader type, several built-in variables are available, listed a
 | const vec3 **SRC_VERTEX** | Model-Space Vertex |
 | const vec3 **SRC_NORMAL** | Model-Space Normal |
 | const vec3 **SRC_TANGENT** | Model-Space Tangent |
+| const float **SRC_BINORMALF** | Direction to Compute Binormal |
 | vec3 **VERTEX** | View-Space Vertex | 
 | vec3 **NORMAL** | View-Space Normal | 
 | vec3 **TANGENT** | View-Space Tangent |