diff --git a/docs/Writing-the-Cyclone-Scheme-Compiler-Revision-1.md b/docs/Writing-the-Cyclone-Scheme-Compiler-Revision-1.md
index 13c82561..1632cc98 100644
--- a/docs/Writing-the-Cyclone-Scheme-Compiler-Revision-1.md
+++ b/docs/Writing-the-Cyclone-Scheme-Compiler-Revision-1.md
@@ -178,7 +178,7 @@ Free variables passed to a nested function must be captured in a closure so they
 
 Cyclone uses flat closures - objects that contain a single function reference and a vector of free variables. This is a more efficient representation than an environment as only a single vector lookup is required to read any of the free variables.
 
-Mutated variables must be added to a pair (called a "cell") by a separate compilation pass executed prior to closure conversion.
+Mutated variables are not directly supported by flat closures and must be added to a pair (called a "cell") by a separate compilation pass prior to closure conversion.
 
 Cyclone's closure conversion is based on code from Marc Feeley's 90 minute Scheme->C compiler and Matt Might's Scheme->C compiler.