diff --git a/grammar/expressions.tex b/grammar/expressions.tex
index 45e5991..6bb37b5 100644
--- a/grammar/expressions.tex
+++ b/grammar/expressions.tex
@@ -30,6 +30,6 @@
     \alt Cons(\x/, \x/) \| nil
     \alt \c/
 
-  <f> ::= \x/ \| \x/ ? \e/
+  <f> ::= \x/ \| \x/ ? \c/
 
 \end{grammar}
diff --git a/grammar/grammar.tex b/grammar/grammar.tex
index 94416db..fb16856 100644
--- a/grammar/grammar.tex
+++ b/grammar/grammar.tex
@@ -32,6 +32,9 @@ modifications:
   \item Let bindings are not recursive by default anymore; a special \emph{let
     rec} construct is introduced equivalent to the recursive \emph{let} of Nix.
 
+  \item Default values in patterns may only be constants. This makes typing of
+    patterns easier, without impact on the expressivity.
+
   \item The last notable change is that the opaque list construct of nix is
     replaced by the classical \texttt{nil} and \texttt{cons}.
     This avoids having over-complicated typing and evaluation rules for lists.
diff --git a/semantics/semantics.tex b/semantics/semantics.tex
index 950974e..6e6949f 100644
--- a/semantics/semantics.tex
+++ b/semantics/semantics.tex
@@ -42,8 +42,8 @@ figure~\pref{fig:semantics:nix-light:patterns}
   \begin{tabular}{rl}
     \eqdefa{\assignp{q@x}{e}}{\assign{x}{e}; \assignp{q}{e}}{}
     \eqdefa{\assignp{(\{ x \} \orthplus q)}{(\{ x = e; \} \orthplus v)}}{\assignp{x}{e}; \assignp{q}{v}}{}
-    \eqdefa{\assignp{(\{ x ? e' \} \orthplus q)}{(\{ x = e; \} \orthplus v)}}{\assignp{x}{e}; \assignp{q}{v}}{}
-    \eqdefa{\assignp{(\{ x ? e \} \orthplus q)}{(v_1 \orthplus v_2)}}{\assignp{x}{e}; \assignp{q}{\left( v_1 \orthplus v_2\right)}}{if $v_1 \neq \{ x = e'; \}$}
+    \eqdefa{\assignp{(\{ x ? c' \} \orthplus q)}{(\{ x = e; \} \orthplus v)}}{\assignp{x}{e}; \assignp{q}{v}}{}
+    \eqdefa{\assignp{(\{ x ? c \} \orthplus q)}{(v_1 \orthplus v_2)}}{\assignp{x}{c}; \assignp{q}{\left( v_1 \orthplus v_2\right)}}{if $v_1 \neq \{ x = e'; \}$}
     \eqdefa{\assignp{\{\}}{\{ \}}}{ø}{}
     \eqdefa{\assignp{\{ .. \}}{v}}{ø}{}
     \eqdefa{\assignp{Cons(x, x')}{Cons(e, e')}}{\assign{x}{e}; \assign{x'}{e'}}{}