diff --git a/src/QMCWaveFunctions/Fermion/MultiDiracDeterminant.2.cpp b/src/QMCWaveFunctions/Fermion/MultiDiracDeterminant.2.cpp
index 643e2204d0..9f8ee6c62f 100644
--- a/src/QMCWaveFunctions/Fermion/MultiDiracDeterminant.2.cpp
+++ b/src/QMCWaveFunctions/Fermion/MultiDiracDeterminant.2.cpp
@@ -443,7 +443,7 @@ void MultiDiracDeterminant::mw_evaluateDetsForPtclMove(const RefVectorWithLeader
 
     PRAGMA_OFFLOAD("omp target teams distribute map(always, from:curRatio_list_ptr[:nw]) \
                     is_device_ptr(psiV_list_devptr, psiMinv_temp_list_devptr)")
-    for (size_t iw = 0; iw < nw; iw++)
+    for (uint32_t iw = 0; iw < nw; iw++)
     {
       ValueType c_ratio = 0.0;
       PRAGMA_OFFLOAD("omp parallel for reduction(+ : c_ratio)")
@@ -780,9 +780,11 @@ void MultiDiracDeterminant::mw_evaluateDetsAndGradsForPtclMove(
       throw std::runtime_error("In MultiDiracDeterminant ompBLAS::copy_batched_offset failed.");
 
 
+    // Index of loop over nw must be 32 bit sized to avoid assignment-after-reduction offload bug
+    // See https://github.com/QMCPACK/qmcpack/issues/4767
     PRAGMA_OFFLOAD("omp target teams distribute is_device_ptr(psiV_list_devptr, psiMinv_temp_list_devptr) \
 		                    map(always, from:curRatio_list_ptr[:nw])")
-    for (size_t iw = 0; iw < nw; iw++)
+    for (uint32_t iw = 0; iw < nw; iw++)
     {
       GradType ratioGradRef_local(0);
       PRAGMA_OFFLOAD("omp parallel for reduction(+ : ratioGradRef_local)")
@@ -1048,7 +1050,7 @@ void MultiDiracDeterminant::mw_evaluateGrads(const RefVectorWithLeader<MultiDira
 
       PRAGMA_OFFLOAD("omp target teams distribute is_device_ptr(psiMinv_list_devptr) \
 		                                  map(always, from: ratioG_list_ptr[:nw])")
-      for (size_t iw = 0; iw < nw; iw++)
+      for (uint32_t iw = 0; iw < nw; iw++)
       {
         ValueType ratioG_local(0);
         PRAGMA_OFFLOAD("omp parallel for reduction(+ : ratioG_local)")
diff --git a/src/QMCWaveFunctions/Fermion/MultiSlaterDetTableMethod.cpp b/src/QMCWaveFunctions/Fermion/MultiSlaterDetTableMethod.cpp
index 809f7ce1ea..d268cbf82a 100644
--- a/src/QMCWaveFunctions/Fermion/MultiSlaterDetTableMethod.cpp
+++ b/src/QMCWaveFunctions/Fermion/MultiSlaterDetTableMethod.cpp
@@ -281,7 +281,7 @@ void MultiSlaterDetTableMethod::mw_evalGrad_impl(const RefVectorWithLeader<WaveF
                     map(from: grad_now_list_ptr[:3 * nw]) \
                     map(always, to: det_value_ptr_list_ptr[:nw]) \
                     map(to: mw_grads_ptr[:mw_grads.size()])")
-    for (size_t iw = 0; iw < nw; iw++)
+    for (uint32_t iw = 0; iw < nw; iw++)
     {
       // enforce full precision reduction due to numerical sensitivity
       PsiValue psi_local(0);
@@ -600,7 +600,7 @@ void MultiSlaterDetTableMethod::mw_calcRatio(const RefVectorWithLeader<WaveFunct
     ScopedTimer local_timer(det_leader.offload_timer);
     PRAGMA_OFFLOAD("omp target teams distribute map(always,from: psi_list_ptr[:nw]) \
           map(always, to: det_value_ptr_list_ptr[:nw])")
-    for (size_t iw = 0; iw < nw; iw++)
+    for (uint32_t iw = 0; iw < nw; iw++)
     {
       PsiValue psi_local(0);
       PRAGMA_OFFLOAD("omp parallel for reduction(+ : psi_local)")