diff --git a/Makefile b/Makefile
index aa2ca0b9..e4c493ef 100644
--- a/Makefile
+++ b/Makefile
@@ -23,6 +23,9 @@ osd: ./libblockstore.so osd_main.cpp osd.h osd_ops.h $(OSD_OBJS)
 stub_osd: stub_osd.o rw_blocking.o
 	g++ $(CXXFLAGS) -o $@ stub_osd.o rw_blocking.o -ltcmalloc_minimal
 
+osd_rmw_test: osd_rmw_test.o
+	g++ $(CXXFLAGS) -o $@ osd_rmw_test.o
+
 STUB_URING_OSD_OBJS := stub_uring_osd.o epoll_manager.o messenger.o msgr_send.o msgr_receive.o ringloop.o timerfd_manager.o json11.o
 stub_uring_osd: $(STUB_URING_OSD_OBJS)
 	g++ $(CXXFLAGS) -o $@ -ltcmalloc_minimal $(STUB_URING_OSD_OBJS) -luring
diff --git a/osd_primary.cpp b/osd_primary.cpp
index 9e0846f3..381eed1e 100644
--- a/osd_primary.cpp
+++ b/osd_primary.cpp
@@ -239,6 +239,12 @@ resume_1:
     {
         cur_op->rmw_buf = calc_rmw(cur_op->buf, op_data->stripes, op_data->prev_set,
             pg.pg_size, pg.pg_minsize, pg.pg_cursize, pg.cur_set.data(), bs_block_size);
+        if (!cur_op->rmw_buf)
+        {
+            // Refuse partial overwrite of an incomplete object
+            cur_op->reply.hdr.retval = -EINVAL;
+            goto continue_others;
+        }
     }
     // Read required blocks
     submit_primary_subops(SUBMIT_RMW_READ, UINT64_MAX, pg.pg_size, op_data->prev_set, cur_op);
@@ -361,10 +367,12 @@ resume_9:
         remove_object_from_state(op_data->oid, op_data->object_state, pg);
         pg.clean_count++;
     }
+    cur_op->reply.hdr.retval = cur_op->req.rw.len;
+continue_others:
     // Remove version override
     pg.ver_override.erase(op_data->oid);
     object_id oid = op_data->oid;
-    finish_op(cur_op, cur_op->req.rw.len);
+    finish_op(cur_op, cur_op->reply.hdr.retval);
     // Continue other write operations to the same object
     auto next_it = pg.write_queue.find(oid);
     auto this_it = next_it;
diff --git a/osd_rmw.cpp b/osd_rmw.cpp
index bbf66604..886de5fd 100644
--- a/osd_rmw.cpp
+++ b/osd_rmw.cpp
@@ -208,7 +208,7 @@ void* calc_rmw(void *request_buf, osd_rmw_stripe_t *stripes, uint64_t *read_osd_
     {
         pg_cursize = 0;
         // Object is degraded/misplaced and will be moved to <write_osd_set>
-        for (int role = 0; role < pg_size; role++)
+        for (int role = 0; role < pg_minsize; role++)
         {
             if (write_osd_set[role] != read_osd_set[role] && write_osd_set[role] != 0)
             {
@@ -228,6 +228,20 @@ void* calc_rmw(void *request_buf, osd_rmw_stripe_t *stripes, uint64_t *read_osd_
                 pg_cursize++;
             }
         }
+        for (int role = pg_minsize; role < pg_size; role++)
+        {
+            if (write_osd_set[role] != read_osd_set[role] && write_osd_set[role] != 0)
+            {
+                for (int r2 = 0; r2 < pg_minsize; r2++)
+                {
+                    cover_read(0, chunk_size, stripes[r2]);
+                }
+            }
+            if (read_osd_set[role] != 0)
+            {
+                pg_cursize++;
+            }
+        }
     }
     if (pg_cursize < pg_size)
     {
@@ -251,8 +265,8 @@ void* calc_rmw(void *request_buf, osd_rmw_stripe_t *stripes, uint64_t *read_osd_
                     }
                     if (found < pg_minsize)
                     {
-                        // FIXME Object is incomplete - refuse partial overwrite
-                        assert(0);
+                        // Object is incomplete - refuse partial overwrite
+                        return NULL;
                     }
                 }
             }
diff --git a/osd_rmw_test.cpp b/osd_rmw_test.cpp
index b5c0f894..84f9dc19 100644
--- a/osd_rmw_test.cpp
+++ b/osd_rmw_test.cpp
@@ -13,6 +13,8 @@ void test6();
 void test7();
 void test8();
 void test9();
+void test10();
+void test11();
 
 /***
 
@@ -91,6 +93,28 @@ Cases:
    }
    + check write0 buffer
 
+10. full overwrite/recovery case:
+   calc_rmw(offset=0, len=256K, read_osd_set=[1,0,0], write_osd_set=[1,2,3])
+   = {
+     read: [ [ 0, 0 ], [ 0, 0 ], [ 0, 0 ] ],
+     write: [ [ 0, 128K ], [ 0, 128K ], [ 0, 128K ] ],
+     input buffer: [ write0, write1 ],
+     rmw buffer: [ write2 ],
+   }
+   then, after calc_rmw_parity_xor(): all the same
+   + check write2 buffer
+
+10. partial recovery case:
+   calc_rmw(offset=128K, len=128K, read_osd_set=[1,0,0], write_osd_set=[1,2,3])
+   = {
+     read: [ [ 0, 128K ], [ 0, 0 ], [ 0, 0 ] ],
+     write: [ [ 0, 0 ], [ 0, 128K ], [ 0, 128K ] ],
+     input buffer: [ write1 ],
+     rmw buffer: [ write2, read0 ],
+   }
+   then, after calc_rmw_parity_xor(): all the same
+   + check write2 buffer
+
 ***/
 
 int main(int narg, char *args[])
@@ -109,6 +133,10 @@ int main(int narg, char *args[])
     test8();
     // Test 9
     test9();
+    // Test 10
+    test10();
+    // Test 11
+    test11();
     // End
     printf("all ok\n");
     return 0;
@@ -361,3 +389,85 @@ void test9()
     check_pattern(stripes[0].write_buf, 128*1024, PATTERN1);
     free(rmw_buf);
 }
+
+void test10()
+{
+    osd_num_t osd_set[3] = { 1, 0, 0 };
+    osd_num_t write_osd_set[3] = { 1, 2, 3 };
+    osd_rmw_stripe_t stripes[3] = { 0 };
+    // Test 10.0
+    split_stripes(2, 128*1024, 0, 256*1024, stripes);
+    assert(stripes[0].req_start == 0 && stripes[0].req_end == 128*1024);
+    assert(stripes[1].req_start == 0 && stripes[1].req_end == 128*1024);
+    assert(stripes[2].req_start == 0 && stripes[2].req_end == 0);
+    // Test 10.1
+    void *write_buf = malloc(256*1024);
+    void *rmw_buf = calc_rmw(write_buf, stripes, osd_set, 3, 2, 3, write_osd_set, 128*1024);
+    assert(rmw_buf);
+    assert(stripes[0].read_start == 0 && stripes[0].read_end == 0);
+    assert(stripes[1].read_start == 0 && stripes[1].read_end == 0);
+    assert(stripes[2].read_start == 0 && stripes[2].read_end == 0);
+    assert(stripes[0].write_start == 0 && stripes[0].write_end == 128*1024);
+    assert(stripes[1].write_start == 0 && stripes[1].write_end == 128*1024);
+    assert(stripes[2].write_start == 0 && stripes[2].write_end == 128*1024);
+    assert(stripes[0].read_buf == NULL);
+    assert(stripes[1].read_buf == NULL);
+    assert(stripes[2].read_buf == NULL);
+    assert(stripes[0].write_buf == write_buf);
+    assert(stripes[1].write_buf == write_buf+128*1024);
+    assert(stripes[2].write_buf == rmw_buf);
+    // Test 10.2
+    set_pattern(stripes[0].write_buf, 128*1024, PATTERN1);
+    set_pattern(stripes[1].write_buf, 128*1024, PATTERN2);
+    calc_rmw_parity_xor(stripes, 3, osd_set, write_osd_set, 128*1024);
+    assert(stripes[0].write_start == 0 && stripes[0].write_end == 128*1024);
+    assert(stripes[1].write_start == 0 && stripes[1].write_end == 128*1024);
+    assert(stripes[2].write_start == 0 && stripes[2].write_end == 128*1024);
+    assert(stripes[0].write_buf == write_buf);
+    assert(stripes[1].write_buf == write_buf+128*1024);
+    assert(stripes[2].write_buf == rmw_buf);
+    check_pattern(stripes[2].write_buf, 128*1024, PATTERN1^PATTERN2);
+    free(rmw_buf);
+    free(write_buf);
+}
+
+void test11()
+{
+    osd_num_t osd_set[3] = { 1, 0, 0 };
+    osd_num_t write_osd_set[3] = { 1, 2, 3 };
+    osd_rmw_stripe_t stripes[3] = { 0 };
+    // Test 11.0
+    split_stripes(2, 128*1024, 128*1024, 256*1024, stripes);
+    assert(stripes[0].req_start == 0 && stripes[0].req_end == 0);
+    assert(stripes[1].req_start == 0 && stripes[1].req_end == 128*1024);
+    assert(stripes[2].req_start == 0 && stripes[2].req_end == 0);
+    // Test 11.1
+    void *write_buf = malloc(256*1024);
+    void *rmw_buf = calc_rmw(write_buf, stripes, osd_set, 3, 2, 3, write_osd_set, 128*1024);
+    assert(rmw_buf);
+    assert(stripes[0].read_start == 0 && stripes[0].read_end == 128*1024);
+    assert(stripes[1].read_start == 0 && stripes[1].read_end == 0);
+    assert(stripes[2].read_start == 0 && stripes[2].read_end == 0);
+    assert(stripes[0].write_start == 0 && stripes[0].write_end == 0);
+    assert(stripes[1].write_start == 0 && stripes[1].write_end == 128*1024);
+    assert(stripes[2].write_start == 0 && stripes[2].write_end == 128*1024);
+    assert(stripes[0].read_buf == rmw_buf+128*1024);
+    assert(stripes[1].read_buf == NULL);
+    assert(stripes[2].read_buf == NULL);
+    assert(stripes[0].write_buf == NULL);
+    assert(stripes[1].write_buf == write_buf);
+    assert(stripes[2].write_buf == rmw_buf);
+    // Test 11.2
+    set_pattern(stripes[0].read_buf, 128*1024, PATTERN1);
+    set_pattern(stripes[1].write_buf, 128*1024, PATTERN2);
+    calc_rmw_parity_xor(stripes, 3, osd_set, write_osd_set, 128*1024);
+    assert(stripes[0].write_start == 0 && stripes[0].write_end == 0);
+    assert(stripes[1].write_start == 0 && stripes[1].write_end == 128*1024);
+    assert(stripes[2].write_start == 0 && stripes[2].write_end == 128*1024);
+    assert(stripes[0].write_buf == NULL);
+    assert(stripes[1].write_buf == write_buf);
+    assert(stripes[2].write_buf == rmw_buf);
+    check_pattern(stripes[2].write_buf, 128*1024, PATTERN1^PATTERN2);
+    free(rmw_buf);
+    free(write_buf);
+}