diff --git a/CorsixTH/Src/th_gfx.h b/CorsixTH/Src/th_gfx.h
index 1400288..7e792a5 100644
--- a/CorsixTH/Src/th_gfx.h
+++ b/CorsixTH/Src/th_gfx.h
@@ -96,14 +96,15 @@ enum THFrameFlags
     THFF_AnimationStart = 1 << 0,
 };
 
+/** Helper structure with parameters to create a #THRenderTarget. */
 struct THRenderTargetCreationParams
 {
-    int iWidth;
-    int iHeight;
-    int iBPP;
-    bool bFullscreen;
-    bool bPresentImmediate;
-    bool bReuseContext;
+    int iWidth;             ///< Expected width of the render target.
+    int iHeight;            ///< Expected height of the render target.
+    int iBPP;               ///< Expected colour depth of the render target.
+    bool bFullscreen;       ///< Run full-screen.
+    bool bPresentImmediate; ///< Whether to present immediately to the user (else wait for Vsync).
+    bool bReuseContext;     ///< (not used)
 };
 
 /*!
diff --git a/CorsixTH/Src/th_lua_gfx.cpp b/CorsixTH/Src/th_lua_gfx.cpp
index 0b9bc2b..f8ea2cb 100644
--- a/CorsixTH/Src/th_lua_gfx.cpp
+++ b/CorsixTH/Src/th_lua_gfx.cpp
@@ -545,6 +545,7 @@ static int l_cursor_position(lua_State *L)
     return 1;
 }
 
+/** Construct the helper structure for making a #THRenderTarget. */
 static THRenderTargetCreationParams l_surface_creation_params(lua_State *L, int iArgStart)
 {
     THRenderTargetCreationParams oParams;
@@ -555,21 +556,18 @@ static THRenderTargetCreationParams l_surface_creation_params(lua_State *L, int
     oParams.bPresentImmediate = false;
     oParams.bReuseContext = false;
 
-#define FLAG(name, field) \
-    else if(stricmp(sOption, name) == 0) \
-        oParams.field = true
-
+    // Parse string arguments, looking for matching parameter names.
     for(int iArg = iArgStart + 2, iArgCount = lua_gettop(L); iArg <= iArgCount; ++iArg)
     {
         const char* sOption = luaL_checkstring(L, iArg);
         if(sOption[0] == 0)
             continue;
-        FLAG("fullscreen",          bFullscreen       );
-        FLAG("present immediate",   bPresentImmediate );
-        FLAG("reuse context",       bReuseContext     );
+
+        if (stricmp(sOption, "fullscreen") == 0)        oParams.bFullscreen       = true;
+        if (stricmp(sOption, "present immediate") == 0) oParams.bPresentImmediate = true;
+        if (stricmp(sOption, "reuse context") == 0)     oParams.bReuseContext     = true;
     }
 
-#undef FLAG
     return oParams;
 }