diff --git a/CMakeLists.txt b/CMakeLists.txt
index 48c742f..ce54f3d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -58,7 +58,7 @@ set(FLAGS
 	-Werror-implicit-function-declaration
 
 	# optimisation level
-	# -Os: small binary
+	# -Os: like -O2 without space-expensive optimizations
 	# -O2: good speed/size tradeoff
 	# -O3: gotta go fast
 	-Os