diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 0a8bdbaf5..dcd734339 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1011,7 +1011,7 @@ void DerivationGoal::outputsSubstituted()
     trace("all outputs substituted (maybe)");
 
     if (nrFailed > 0 && nrFailed > nrNoSubstituters + nrIncompleteClosure && !settings.tryFallback)
-        throw Error(format("some substitutes for the outputs of derivation `%1%' failed; try `--fallback'") % drvPath);
+        throw Error(format("some substitutes for the outputs of derivation `%1%' failed (usually happens due to networking issues); try `--fallback' to build derivation from source ") % drvPath);
 
     /*  If the substitutes form an incomplete closure, then we should
         build the dependencies of this derivation, but after that, we