diff --git a/source/compatibility.tex b/source/compatibility.tex
index 081b113306..185dc4f835 100644
--- a/source/compatibility.tex
+++ b/source/compatibility.tex
@@ -365,7 +365,7 @@
 
 struct D : private B {
   void f(std::set<B, std::less<>>& s) {
-    s.erase(*this);             // ill formed; previously well-formed
+    s.erase(*this);             // ill-formed; previously well-formed
   }
 };
 \end{codeblock}