diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index b63584f28..ef8c2811b 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -581,7 +581,8 @@ void LocalStore::checkDerivationOutputs(const Path & drvPath, const Derivation &
 uint64_t LocalStore::addValidPath(State & state,
     const ValidPathInfo & info, bool checkOutputs)
 {
-    assert(info.ca == "" || info.isContentAddressed(*this));
+    if (info.ca != "" && !info.isContentAddressed(*this))
+        throw Error("cannot add path '%s' to the Nix store because it claims to be content-addressed but isn't", info.path);
 
     state.stmtRegisterValidPath.use()
         (info.path)