diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 2ba79ec46..589b449d0 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -1993,7 +1993,7 @@ void LocalDerivationGoal::runChild()
                 else if (drv->builder == "builtin:unpack-channel")
                     builtinUnpackChannel(drv2);
                 else
-                    throw Error("unsupported builtin function '%1%'", string(drv->builder, 8));
+                    throw Error("unsupported builtin builder '%1%'", string(drv->builder, 8));
                 _exit(0);
             } catch (std::exception & e) {
                 writeFull(STDERR_FILENO, e.what() + std::string("\n"));