diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index e1ec87d3b..6743d7fd8 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -35,7 +35,6 @@ struct Env;
 struct Expr;
 struct ExprLambda;
 struct PrimOp;
-struct PrimOp;
 class Symbol;
 struct Pos;
 class EvalState;