diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index e68d1a2a5..f48d003fc 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -167,7 +167,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
             else if (n == "name")
                 name = state.forceStringNoCtx(*attr.value, *attr.pos);
             else
-                throw EvalError("unsupported argument '%s' to 'fetchGit', at %s", attr.name, *attr.pos);
+                throw EvalError("unsupported argument '%s' to 'fetchMercurial', at %s", attr.name, *attr.pos);
         }
 
         if (url.empty())