diff --git a/doc/mrbconf/README.md b/doc/mrbconf/README.md
index 9532681eb..813b80839 100644
--- a/doc/mrbconf/README.md
+++ b/doc/mrbconf/README.md
@@ -78,6 +78,6 @@ will be defined as `mrb_int`.
 * Useful tracking unnecessary mruby object allocation.
 
 `MRB_GC_ARENA_SIZE`
-* Default value 100.
+* Default value is 100.
 * Ignored when `MRB_GC_FIXED_ARENA` isn't defined.
 * Defines fixed GC arena size.