diff --git a/Source/reactions/Castro_react.cpp b/Source/reactions/Castro_react.cpp
index 73c5a3c873..f4f4421206 100644
--- a/Source/reactions/Castro_react.cpp
+++ b/Source/reactions/Castro_react.cpp
@@ -533,7 +533,9 @@ Castro::react_state(Real time, Real dt)
 #endif
     int num_failed = 0;
 
-    // why no omp here?
+#ifdef _OPENMP
+#pragma omp parallel reduction(+:num_failed)
+#endif
     for (MFIter mfi(S_new, TilingIfNotGPU()); mfi.isValid(); ++mfi)
     {
         const Box& bx = mfi.growntilebox(ng);