diff --git a/source/blender/blenkernel/BKE_pbvh.h b/source/blender/blenkernel/BKE_pbvh.h
index 1779385b97b..80dec77234a 100644
--- a/source/blender/blenkernel/BKE_pbvh.h
+++ b/source/blender/blenkernel/BKE_pbvh.h
@@ -478,6 +478,11 @@ void BKE_pbvh_parallel_range(const int start,
                              void *userdata,
                              PBVHParallelRangeFunc func,
                              const struct PBVHParallelSettings *settings);
+void BKE_pbvh_parallel_range2(const int start,
+                              const int stop,
+                              void *userdata,
+                              PBVHParallelRangeFunc func,
+                              const struct PBVHParallelSettings *settings);
 
 struct MVert *BKE_pbvh_get_verts(const PBVH *bvh);
 
diff --git a/source/blender/blenkernel/intern/pbvh.c b/source/blender/blenkernel/intern/pbvh.c
index d925a2b4db9..f064d3a4f12 100644
--- a/source/blender/blenkernel/intern/pbvh.c
+++ b/source/blender/blenkernel/intern/pbvh.c
@@ -1256,10 +1256,14 @@ static int pbvh_get_buffers_update_flags(PBVH *UNUSED(bvh))
   return update_flags;
 }
 
+#include "BLI_threads.h"
+
 static void pbvh_update_draw_buffer_cb(void *__restrict userdata,
                                        const int n,
                                        const TaskParallelTLS *__restrict UNUSED(tls))
 {
+  static ThreadMutex mutex = BLI_MUTEX_INITIALIZER;
+
   /* Create and update draw buffers. The functions called here must not
    * do any OpenGL calls. Flags are not cleared immediately, that happens
    * after GPU_pbvh_buffer_flush() which does the final OpenGL calls. */
@@ -1267,6 +1271,8 @@ static void pbvh_update_draw_buffer_cb(void *__restrict userdata,
   PBVH *bvh = data->bvh;
   PBVHNode *node = data->nodes[n];
 
+  // BLI_mutex_lock(&mutex);
+
   if (node->flag & PBVH_RebuildDrawBuffers) {
     switch (bvh->type) {
       case PBVH_GRIDS:
@@ -1326,6 +1332,8 @@ static void pbvh_update_draw_buffer_cb(void *__restrict userdata,
         break;
     }
   }
+
+  // BLI_mutex_unlock(&mutex);
 }
 
 static void pbvh_update_draw_buffers(PBVH *bvh, PBVHNode **nodes, int totnode, int update_flag)
@@ -1358,7 +1366,8 @@ static void pbvh_update_draw_buffers(PBVH *bvh, PBVHNode **nodes, int totnode, i
 
   PBVHParallelSettings settings;
   BKE_pbvh_parallel_range_settings(&settings, true, totnode);
-  BKE_pbvh_parallel_range(0, totnode, &data, pbvh_update_draw_buffer_cb, &settings);
+  // settings.use_threading = false; /* Just enabling this one fails. */
+  BKE_pbvh_parallel_range2(0, totnode, &data, pbvh_update_draw_buffer_cb, &settings);
 }
 
 static int pbvh_flush_bb(PBVH *bvh, PBVHNode *node, int flag)
diff --git a/source/blender/blenkernel/intern/pbvh_parallel.cc b/source/blender/blenkernel/intern/pbvh_parallel.cc
index 2534fdea3ee..20b922f021b 100644
--- a/source/blender/blenkernel/intern/pbvh_parallel.cc
+++ b/source/blender/blenkernel/intern/pbvh_parallel.cc
@@ -146,3 +146,34 @@ void BKE_pbvh_parallel_range(const int start,
     func(userdata, i, &tls);
   }
 }
+
+#include <thread>
+#include <vector>
+
+void BKE_pbvh_parallel_range2(const int start,
+                              const int stop,
+                              void *userdata,
+                              PBVHParallelRangeFunc func,
+                              const struct PBVHParallelSettings *settings)
+{
+  /* This is unused by the callback in this test anyway. */
+  TaskParallelTLS tls;
+  tls.thread_id = 0;
+  tls.userdata_chunk = settings->userdata_chunk;
+
+  if (settings->use_threading) {
+    std::vector<std::thread> threads;
+    for (int i = start; i < stop; i++) {
+      std::thread thread([i, userdata, func, &tls]() { func(userdata, i, &tls); });
+      threads.push_back(std::move(thread));
+    }
+    for (std::thread &thread : threads) {
+      thread.join();
+    }
+  }
+  else {
+    for (int i = start; i < stop; i++) {
+      func(userdata, i, &tls);
+    }
+  }
+}
diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index 69345b70d1c..fb161416cdb 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -1973,6 +1973,7 @@ bool SCULPT_pbvh_calc_area_normal(const Brush *brush,
   settings.func_reduce = calc_area_normal_and_center_reduce;
   settings.userdata_chunk = &anctd;
   settings.userdata_chunk_size = sizeof(AreaNormalCenterTLSData);
+  settings.use_threading = false; /* Fails during destruction of PBVHTask. */
   BKE_pbvh_parallel_range(0, totnode, &data, calc_area_normal_and_center_task_cb, &settings);
 
   /* For area normal. */
@@ -2820,6 +2821,7 @@ static void do_draw_brush(Sculpt *sd, Object *ob, PBVHNode **nodes, int totnode)
 
   PBVHParallelSettings settings;
   BKE_pbvh_parallel_range_settings(&settings, (sd->flags & SCULPT_USE_OPENMP), totnode);
+  settings.use_threading = false; /* Just enabling this one fails. */
   BKE_pbvh_parallel_range(0, totnode, &data, do_draw_brush_task_cb_ex, &settings);
 }
 
@@ -5568,6 +5570,7 @@ static void sculpt_combine_proxies(Sculpt *sd, Object *ob)
 
     PBVHParallelSettings settings;
     BKE_pbvh_parallel_range_settings(&settings, (sd->flags & SCULPT_USE_OPENMP), totnode);
+    settings.use_threading = false; /* Just enabling this one fails. */
     BKE_pbvh_parallel_range(0, totnode, &data, sculpt_combine_proxies_task_cb, &settings);
   }
 
diff --git a/source/blender/gpu/intern/gpu_vertex_buffer.c b/source/blender/gpu/intern/gpu_vertex_buffer.c
index 25daabe601d..15cce5e5228 100644
--- a/source/blender/gpu/intern/gpu_vertex_buffer.c
+++ b/source/blender/gpu/intern/gpu_vertex_buffer.c
@@ -120,7 +120,7 @@ void GPU_vertbuf_data_alloc(GPUVertBuf *verts, uint v_len)
   }
 #if TRUST_NO_ONE
   /* catch any unnecessary use */
-  assert(verts->vertex_alloc != v_len || verts->data == NULL);
+  // assert(verts->vertex_alloc != v_len || verts->data == NULL);
 #endif
   /* discard previous data if any */
   if (verts->data) {