diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 06bf671e2a..f1a600103d 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -56,6 +56,7 @@ static Expr substArgs(EvalState & state,
 
         ATermList valids;
         if (matchValidValues(valids2, valids)) {
+            value = evalExpr(state, value);
             bool found = false;
             for (ATermIterator j(valids); j; ++j) {
                 Expr v = evalExpr(state, *j);