diff --git a/lsm/include/lsm/store.h b/lsm/include/lsm/store.h
index 7e7e59a..1ddf6cc 100644
--- a/lsm/include/lsm/store.h
+++ b/lsm/include/lsm/store.h
@@ -108,8 +108,9 @@ lsm_error lsm_store_open_read(lsm_entry_handle **out, lsm_store *store,
                               lsm_str *key);
 
 /**
- * Open a write handle to the given entry.  This entry must be properly closed
- * using `lsm_store_handle_close`.
+ * Open a write handle to the given entry. This handle should only be used for
+ * writing; read operations on this handle are unsupported. This entry must be
+ * properly closed using `lsm_store_handle_close`.
  *
  * @param out pointer to store handle pointer
  * @param store store to retrieve entry from
diff --git a/lsm/src/store/lsm_store.c b/lsm/src/store/lsm_store.c
index 27ebf68..42643b9 100644
--- a/lsm/src/store/lsm_store.c
+++ b/lsm/src/store/lsm_store.c
@@ -132,7 +132,7 @@ lsm_error lsm_store_open_write(lsm_entry_handle **out, lsm_store *store,
     sprintf(path, "%s/%s", lsm_str_ptr(store->data_path),
             lsm_str_ptr(entry->key));
 
-    FILE *f = fopen(path, "wb");
+    FILE *f = fopen(path, "ab");
 
     if (f == NULL) {
       free(handle);
@@ -184,6 +184,10 @@ lsm_error lsm_store_insert(lsm_entry_handle **out, lsm_store *store,
 
 lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
                                 lsm_str *data) {
+  if (lsm_str_len(data) == 0) {
+    return lsm_error_ok;
+  }
+
   lsm_entry *entry = handle->wrapper->entry;
 
   uint64_t new_len = entry->data.len + lsm_str_len(data);
@@ -199,7 +203,6 @@ lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
 
     memcpy(&buf[entry->data.len], data_s, lsm_str_len(data));
     entry->data.value.ptr = buf;
-    entry->data.len = new_len;
   }
   // Data will end up on disk
   else {
@@ -215,10 +218,19 @@ lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
         return lsm_error_failed_io;
       }
 
+      size_t written = 0;
+
+      // Write original in-memory data to file
+      while (written < entry->data.len) {
+        written += fwrite(&entry->data.value.ptr[written], sizeof(char),
+                          entry->data.len - written, f);
+      }
+
+      free(entry->data.value.ptr);
+      entry->data.value.ptr = NULL;
+
       handle->f = f;
       entry->data.on_disk = true;
-
-      // TODO free old buff, write original data to file
     }
 
     size_t written = 0;
@@ -230,5 +242,7 @@ lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
     }
   }
 
+  entry->data.len = new_len;
+
   return lsm_error_ok;
 }