diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index d371a3fb8..402de78ad 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -600,8 +600,6 @@ void EvalState::addConstant(const string & name, Value * v)
 Value * EvalState::addPrimOp(const string & name,
     size_t arity, PrimOpFun primOp)
 {
-    assert(arity <= maxPrimOpArity);
-
     auto name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
     Symbol sym = symbols.create(name2);
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 65cf04b57..1aab8e166 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -279,8 +279,6 @@ private:
 
     void addConstant(const string & name, Value * v);
 
-    constexpr static size_t maxPrimOpArity = 3;
-
     Value * addPrimOp(const string & name,
         size_t arity, PrimOpFun primOp);