diff --git a/tabulator-mpi/source.cpp b/tabulator-mpi/source.cpp
index ed9c239..f7fe54f 100644
--- a/tabulator-mpi/source.cpp
+++ b/tabulator-mpi/source.cpp
@@ -28,7 +28,7 @@ int main(int argc, char **argv) {
   MPI_Comm_size(MPI_COMM_WORLD, &size);
 
   if (size < 2)
-    error("this must be run under mpi with at least two processes.", rank);
+    return error("this must be run under mpi with at least two processes.", rank);
 
   std::vector<std::string> filenames = {};
   int rounds_per_chunk = default_rounds_per_chunk;