diff --git a/builtin_function.cpp b/builtin_function.cpp
index 1d847a6..b7719ab 100644
--- a/builtin_function.cpp
+++ b/builtin_function.cpp
@@ -1118,6 +1118,27 @@
    "       (declare (in) vec4 arg1)\n"
    "       (declare (in) vec4 arg2))\n"
    "     ((return (expression vec4 + (expression vec4 * (var_ref arg0) (expression vec4 - (constant float (1.000000)) (var_ref arg2))) (expression vec4 * (var_ref arg1) (var_ref arg2))))))\n"
+   "\n"
+   "   (signature vec2\n"
+   "     (parameters\n"
+   "       (declare (in) vec2 arg0)\n"
+   "       (declare (in) vec2 arg1)\n"
+   "       (declare (in) float arg2))\n"
+   "     ((return (expression vec2 + (expression vec2 * (var_ref arg0) (expression vec2 - (constant float (1.000000)) (var_ref arg2))) (expression vec2 * (var_ref arg1) (var_ref arg2))))))\n"
+   "\n"
+   "   (signature vec3\n"
+   "     (parameters\n"
+   "       (declare (in) vec3 arg0)\n"
+   "       (declare (in) vec3 arg1)\n"
+   "       (declare (in) float arg2))\n"
+   "     ((return (expression vec3 + (expression vec3 * (var_ref arg0) (expression vec3 - (constant float (1.000000)) (var_ref arg2))) (expression vec3 * (var_ref arg1) (var_ref arg2))))))\n"
+   "\n"
+   "   (signature vec4\n"
+   "     (parameters\n"
+   "       (declare (in) vec4 arg0)\n"
+   "       (declare (in) vec4 arg1)\n"
+   "       (declare (in) float arg2))\n"
+   "     ((return (expression vec4 + (expression vec4 * (var_ref arg0) (expression vec4 - (constant float (1.000000)) (var_ref arg2))) (expression vec4 * (var_ref arg1) (var_ref arg2))))))\n"
    "))\n"
 };