diff --git a/commands/command_divelist.cpp b/commands/command_divelist.cpp
index 6f2887056..fe8f6050f 100644
--- a/commands/command_divelist.cpp
+++ b/commands/command_divelist.cpp
@@ -419,7 +419,7 @@ AddDive::AddDive(dive *d, bool autogroup, bool newNumber)
 
 	int idx = divelog.dives.get_insertion_index(divePtr.get());
 	if (newNumber)
-		divePtr->number = get_dive_nr_at_idx(idx);
+		divePtr->number = divelog.dives.get_dive_nr_at_idx(idx);
 
 	divesToAdd.dives.push_back({ std::move(divePtr), trip, site });
 	if (allocTrip)
diff --git a/core/divelist.cpp b/core/divelist.cpp
index 4dfa8d022..13d3419fd 100644
--- a/core/divelist.cpp
+++ b/core/divelist.cpp
@@ -1142,13 +1142,6 @@ process_imported_dives_result process_imported_dives(struct divelog &import_log,
 	return res;
 }
 
-static struct dive *get_last_valid_dive()
-{
-	auto it = std::find_if(divelog.dives.rbegin(), divelog.dives.rend(),
-			      [](auto &d) { return !d->invalid; });
-	return it != divelog.dives.rend() ? it->get() : nullptr;
-}
-
 /* return the number a dive gets when inserted at the given index.
  * this function is supposed to be called *before* a dive was added.
  * this returns:
@@ -1156,14 +1149,14 @@ static struct dive *get_last_valid_dive()
  * 	- last_nr+1 for addition at end of log (if last dive had a number)
  * 	- 0 for all other cases
  */
-int get_dive_nr_at_idx(int idx)
+int dive_table::get_dive_nr_at_idx(int idx) const
 {
-	if (static_cast<size_t>(idx) < divelog.dives.size())
+	if (static_cast<size_t>(idx) < size())
 		return 0;
-	struct dive *last_dive = get_last_valid_dive();
-	if (!last_dive)
+	auto it = std::find_if(rbegin(), rend(), [](auto &d) { return !d->invalid; });
+	if (it == rend())
 		return 1;
-	return last_dive->number ? last_dive->number + 1 : 0;
+	return (*it)->number ? (*it)->number + 1 : 0;
 }
 
 /* lookup of trip in main trip_table based on its id */
diff --git a/core/divelist.h b/core/divelist.h
index 2942c9da1..e4b5dd303 100644
--- a/core/divelist.h
+++ b/core/divelist.h
@@ -21,6 +21,7 @@ struct dive_table : public sorted_owning_table<dive, &comp_dives> {
 	void record_dive(std::unique_ptr<dive> d);	// call fixup_dive() before adding dive to table.
 	std::unique_ptr<dive> unregister_dive(int idx);
 
+	int get_dive_nr_at_idx(int idx) const;
 	timestamp_t get_surface_interval(timestamp_t when) const;
 	struct dive *find_next_visible_dive(timestamp_t when);
 };
@@ -51,7 +52,6 @@ struct process_imported_dives_result {
 extern process_imported_dives_result process_imported_dives(struct divelog &import_log, int flags);
 
 extern void get_dive_gas(const struct dive *dive, int *o2_p, int *he_p, int *o2low_p);
-extern int get_dive_nr_at_idx(int idx);
 
 int get_min_datafile_version();
 void report_datafile_version(int version);