diff --git a/image_analysis/scale_merge/RotationScaleMerge.cpp b/image_analysis/scale_merge/RotationScaleMerge.cpp
index ffc7281e..37d8313d 100644
--- a/image_analysis/scale_merge/RotationScaleMerge.cpp
+++ b/image_analysis/scale_merge/RotationScaleMerge.cpp
@@ -1456,7 +1456,8 @@ RotationScaleMerge::Result RotationScaleMerge::MergeAndStats(int n_groups, bool
 
     // The em-stats / samples / merge-accumulate / R_meas reductions run on the resident, scaled fulls
     // (their group CSR is still on the device from scale-fulls) when fulls_resident; the host keeps the
-    // I2-sort, the (a,b) fit, the export and the statistics. reject_outliers is excluded upstream.
+    // I2-sort, the (a,b) fit, the export and the statistics. Outlier rejection runs on the device too,
+    // and MergeAccum hands the per-full flags back so the host-side reductions see the same rejections.
     bool use_gpu_merge = false;
 #ifdef JFJOCH_USE_CUDA
     use_gpu_merge = fulls_resident && !fulls.empty();
@@ -1656,7 +1657,7 @@ RotationScaleMerge::Result RotationScaleMerge::MergeAndStats(int n_groups, bool
     struct Accum { double swI = 0, sw = 0, swIh[2] = {0, 0}, swh[2] = {0, 0}; size_t nh[2] = {0, 0}; float d = NAN; };
     std::vector<Accum> acc(n_groups);
     size_t reject_count = 0;
-    std::vector<char> rejected_obs(fulls.size(), 0);   // per-full outlier-rejected flag (mirrors the GPU path)
+    std::vector<uint8_t> rejected_obs(fulls.size(), 0);   // per-full outlier-rejected flag (both paths)
     bool did_gpu_acc = false;
 #ifdef JFJOCH_USE_CUDA
     if (use_gpu_merge) {
@@ -1666,7 +1667,8 @@ RotationScaleMerge::Result RotationScaleMerge::MergeAndStats(int n_groups, bool
         gpu_->MergeAccum(error_model_a, error_model_b, error_model_active,
                          reject_outliers, reject_nsigma, reject_median.data(),
                          aswI.data(), asw.data(), aswIh0.data(), aswIh1.data(),
-                         aswh0.data(), aswh1.data(), anh0.data(), anh1.data(), ad.data(), arej.data());
+                         aswh0.data(), aswh1.data(), anh0.data(), anh1.data(), ad.data(), arej.data(),
+                         rejected_obs.data());
         for (int g = 0; g < n_groups; ++g) {
             Accum &a = acc[g];
             a.swI = aswI[g]; a.sw = asw[g]; a.swIh[0] = aswIh0[g]; a.swIh[1] = aswIh1[g];
@@ -1857,7 +1859,7 @@ RotationScaleMerge::Result RotationScaleMerge::MergeAndStats(int n_groups, bool
         anom.reserve(result.merged.size() * 2 + 1);
         for (const auto &o : fulls) {
             if (!usable_merge(o)) continue;
-            if (rejected_obs[&o - fulls.data()]) continue;   // outlier-rejected in the merge (CPU path)
+            if (rejected_obs[&o - fulls.data()]) continue;   // outlier-rejected in the merge
             const HKLKey ak = anom_keygen(o.h, o.k, o.l);
             const int hand = ak.plus ? 0 : 1;
             const float I_corr = o.I * o.corr;
diff --git a/image_analysis/scale_merge/RotationScaleMergeGPU.cu b/image_analysis/scale_merge/RotationScaleMergeGPU.cu
index 9b8123f4..676f3243 100644
--- a/image_analysis/scale_merge/RotationScaleMergeGPU.cu
+++ b/image_analysis/scale_merge/RotationScaleMergeGPU.cu
@@ -788,7 +788,7 @@ void RotationScaleMergeGPU::MergeAccum(double error_model_a, double error_model_
                                        bool reject_outliers, double reject_nsigma, const float *reject_median,
                                        double *swI, double *sw, double *swIh0, double *swIh1,
                                        double *swh0, double *swh1, int32_t *nh0, int32_t *nh1, double *d_out,
-                                       int32_t *rejected) {
+                                       int32_t *rejected, uint8_t *rejected_obs) {
     auto &d = *impl_;
     const int ng = d.n_groups;
     d.a_swI = CudaDevicePtr<double>(std::max(1, ng)); d.a_sw = CudaDevicePtr<double>(std::max(1, ng));
@@ -829,6 +829,8 @@ void RotationScaleMergeGPU::MergeAccum(double error_model_a, double error_model_
     CudaCheck(cudaMemcpy(nh0, d.a_nh0.get(), size_t(ng) * sizeof(int32_t), cudaMemcpyDeviceToHost), "dl nh0");
     CudaCheck(cudaMemcpy(nh1, d.a_nh1.get(), size_t(ng) * sizeof(int32_t), cudaMemcpyDeviceToHost), "dl nh1");
     CudaCheck(cudaMemcpy(rejected, d.a_rejected.get(), size_t(ng) * sizeof(int32_t), cudaMemcpyDeviceToHost), "dl rej");
+    CudaCheck(cudaMemcpy(rejected_obs, d.m_rejected.get(), size_t(d.n_fulls) * sizeof(uint8_t), cudaMemcpyDeviceToHost),
+              "dl rejected_obs");
 }
 
 void RotationScaleMergeGPU::MergeRmeas(const double *merged_I, double *absdev, double *sumI,
diff --git a/image_analysis/scale_merge/RotationScaleMergeGPU.h b/image_analysis/scale_merge/RotationScaleMergeGPU.h
index 79a0bcaa..b5c3d37a 100644
--- a/image_analysis/scale_merge/RotationScaleMergeGPU.h
+++ b/image_analysis/scale_merge/RotationScaleMergeGPU.h
@@ -73,12 +73,14 @@ public:
 
     // Per-group merge accumulators (inv-var sums + deterministic half-sets, error-model-corrected sigma
     // from a/b). Outputs length n_groups; rejected[g] counts outliers dropped (reject_median uploaded, NAN
-    // where none). Requires MergeEmSamples first (em_mean resident).
+    // where none). rejected_obs is the per-full flag (length n_fulls): the host needs it for the reductions
+    // it still does itself, above all the anomalous I(+)/I(-) split.
+    // Requires MergeEmSamples first (em_mean resident).
     void MergeAccum(double error_model_a, double error_model_b, bool error_model_active,
                     bool reject_outliers, double reject_nsigma, const float *reject_median,
                     double *swI, double *sw, double *swIh0, double *swIh1,
                     double *swh0, double *swh1, int32_t *nh0, int32_t *nh1, double *d_out,
-                    int32_t *rejected);
+                    int32_t *rejected, uint8_t *rejected_obs);
 
     // Per-group R_meas accumulators (sum|I_corr-merged_I|, sum_I, n, and the usable count for per-shell
     // total_observations); merged_I is uploaded. All arrays length n_groups.