diff --git a/glslang/Include/glslang_c_shader_types.h b/glslang/Include/glslang_c_shader_types.h
index f11443f3b..dc9009f30 100644
--- a/glslang/Include/glslang_c_shader_types.h
+++ b/glslang/Include/glslang_c_shader_types.h
@@ -121,7 +121,9 @@ typedef enum {
 /* EShExecutable counterpart */
 typedef enum { GLSLANG_EX_VERTEX_FRAGMENT, GLSLANG_EX_FRAGMENT } glslang_executable_t;
 
-/* EShOptimizationLevel counterpart  */
+// EShOptimizationLevel counterpart
+// This enum is not used in the current C interface, but could be added at a later date.
+// GLSLANG_OPT_NONE is the current default.
 typedef enum {
     GLSLANG_OPT_NO_GENERATION,
     GLSLANG_OPT_NONE,