diff --git a/lib/Biodiverse/Randomise.pm b/lib/Biodiverse/Randomise.pm
index 25b209368..9164eefde 100644
--- a/lib/Biodiverse/Randomise.pm
+++ b/lib/Biodiverse/Randomise.pm
@@ -1387,6 +1387,7 @@ sub get_spatial_output_for_label_allocation {
     my ($self, %args) = @_;
     
     my $sp_conditions = $args{spatial_conditions_for_label_allocation};
+    my $param_name = $args{param_name} // 'SPATIAL_OUTPUT_FOR_LABEL_ALLOCATION';
     
     return if !defined $sp_conditions;
 
@@ -1409,7 +1410,7 @@ sub get_spatial_output_for_label_allocation {
 
     return if !length $sp_check_text; #  all we had was whitespace and comments
 
-    my $sp = $self->get_param('SPATIAL_OUTPUT_FOR_LABEL_ALLOCATION');
+    my $sp = $self->get_param($param_name);
     
     return $sp if $sp;
 
@@ -1423,6 +1424,7 @@ sub get_spatial_output_for_label_allocation {
             #definition_query   => $def_query,  #  do we want a def query for this?  Prob not.  
             calculations       => [],
             override_valid_analysis_check => 1,
+            elements_to_calc              => $args{elements_to_calc},
             calc_only_elements_to_calc    => 1,  #  really need to rename this undocumented arg
         );
     };
@@ -1432,7 +1434,7 @@ sub get_spatial_output_for_label_allocation {
     
     croak $e if $e;
 
-    $self->set_param(SPATIAL_OUTPUT_FOR_LABEL_ALLOCATION => $sp);
+    $self->set_param($param_name => $sp);
 
     return $sp;
 }
diff --git a/lib/Biodiverse/Randomise/CurveBall.pm b/lib/Biodiverse/Randomise/CurveBall.pm
index abc68bcb7..0e95e4f1a 100644
--- a/lib/Biodiverse/Randomise/CurveBall.pm
+++ b/lib/Biodiverse/Randomise/CurveBall.pm
@@ -6,6 +6,8 @@ use 5.022;
 
 our $VERSION = '4.99_002';
 
+use Carp qw /croak/;
+
 use experimental 'refaliasing';
 use experimental 'declared_refs';
 no warnings 'experimental::refaliasing';
@@ -145,6 +147,44 @@ END_PROGRESS_TEXT
 
     $progress_bar->reset;
 
+    my (%sp_swap_list, @gps_with_nbrs);
+    if (my $sp_conditions = $args{spatial_condition_for_swap_pairs}) {
+        my $sp_swapper = $self->get_spatial_output_for_label_allocation (
+            %args,
+            spatial_conditions_for_label_allocation => $sp_conditions,
+            param_name                              => 'SPATIAL_OUTPUT_FOR_SWAP_CANDIDATES',
+            elements_to_calc                        => \@sorted_groups,  #  excludes empty and full groups
+        );
+        if ($sp_swapper) {
+            my $spatial_conditions_arr = $sp_swapper->get_spatial_conditions;
+            my $sp_cond_obj = $spatial_conditions_arr->[0];
+            my $result_type = $sp_cond_obj->get_result_type;
+            if ($result_type eq 'always_true') {
+                say "[Randomise] spatial condition always_true, reverting to non-spatial allocation";
+            }
+            elsif ($result_type =~ /^always_false|self_only$/) {
+                croak "Spatial condition means it is impossible for groups to have neighbours, "
+                    . "so cannot swap labels with neighbours"
+                      if !@gps_with_nbrs;
+            }
+            else {
+                foreach my $element ($sp_swapper->get_element_list) {
+                    my $nbrs = $sp_swapper->get_list_ref_aa ($element, '_NBR_SET1') // [];
+                    #  prefilter the focal group
+                    my @filtered = sort grep {$_ ne $element} @$nbrs;
+                    next if !@filtered;
+                    $sp_swap_list{$element} = \@filtered;
+                }
+                @gps_with_nbrs = sort keys %sp_swap_list;
+                my $n_gps_w_nbrs = @gps_with_nbrs;
+                say "[Randomise] $n_gps_w_nbrs of $n_groups groups have swappable neighbours";
+                croak "No groups have neighbours, cannot swap labels with neighbours"
+                    if !@gps_with_nbrs;
+            }
+        }
+    }
+    my $use_spatial_swap = !!%sp_swap_list;
+
     #  Basic algorithm:
     #  pick two different groups at random
     #  swap as many labels as possible
@@ -169,12 +209,24 @@ END_PROGRESS_TEXT
     ) {
         $attempts++;
 
-        my $group1 = $sorted_groups[int $rand->rand ($n_groups)];
-        my $group2 = $sorted_groups[int $rand->rand ($n_groups)];
-        while ($group1 eq $group2) {
-            #  handle pathological case of only one group
-            last MAIN_ITER if $n_groups == 1;
-            $group2 = $sorted_groups[int $rand->rand ($n_groups)];
+        #  handle pathological case of only one group
+        last MAIN_ITER if $n_groups == 1;
+
+        my $group1; ;
+        my $group2;
+        if ($use_spatial_swap) {
+            $group1 = $gps_with_nbrs[int $rand->rand (scalar @gps_with_nbrs)];
+            my $n = scalar @{$sp_swap_list{$group1}};
+            next MAIN_ITER if !$n;
+            #  we have already filtered group1 from its list
+            $group2 = $sp_swap_list{$group1}[int $rand->rand($n)]
+        }
+        else {
+            $group1 = $sorted_groups[int $rand->rand ($n_groups)];
+            $group2 = $sorted_groups[int $rand->rand($n_groups)];
+            while ($group1 eq $group2) {  #  keep trying - a bit wasteful but should be rare
+                $group2 = $sorted_groups[int $rand->rand($n_groups)];
+            }
         }
 
         my \%labels1 = $lb_hash{$group1};
diff --git a/t/28-Randomisation.t b/t/28-Randomisation.t
index cccb862dc..a3ce28e9c 100644
--- a/t/28-Randomisation.t
+++ b/t/28-Randomisation.t
@@ -125,15 +125,45 @@ sub test_rand_independent_swaps_modified {
 
 sub test_rand_curveball {
     test_rand_structured_richness_same (
-        'rand_curveball', swap_count => 1000,
+        'rand_curveball',
     );
 }
 
+sub test_rand_curveball_sp_cond {
+    my $rand_bd_array = test_rand_structured_richness_same (
+        'rand_curveball',
+        spatial_condition_for_swap_pairs => 'sp_circle(radius => 100000)',
+        resolution => 100000,
+        log_suffix => ' with spatial condition'
+    );
+
+    #  The site data have these groups as an isolated set.  There should only be swapping among them
+    #  so the total counts will be constant across realisations.
+    my $expected = {
+        'Genus:sp1' =>  4,
+        'Genus:sp2' => 10,
+        'Genus:sp3' =>  4,
+    };
+    my $i;
+    foreach my $bd (@$rand_bd_array) {
+        $i++;
+        my %collated_labels;
+        foreach my $gp (qw /3250000:3050000 3150000:2950000 3250000:2950000 3250000:2850000/) {
+            my $labels = $bd->get_labels_in_group_as_hash (group => $gp);
+            foreach my $label (keys %$labels) {
+                $collated_labels{$label} += $labels->{$label};
+            }
+        }
+        is \%collated_labels, $expected, "Curveball spatial: labels and counts for isolated subregion, rand bd $i";
+    }
+}
+
 sub test_rand_structured_richness_same {
     my ($rand_function, %args) = @_;
     $rand_function //= 'rand_structured';
+    my $log_suffix = delete $args{log_suffix} // '';
     
-    my $c = 100000;
+    my $c  = delete $args{resolution} // 100000;
     my $bd = get_basedata_object_from_site_data(CELL_SIZES => [$c, $c]);
 
     #  add some empty groups - need enough to trigger issue #543
@@ -152,6 +182,7 @@ sub test_rand_structured_richness_same {
             $bd->add_element(group => $gp, label => $label);
         }
     }
+    $bd->build_spatial_index (resolutions => [$c, $c]);
 
     #  name is short for test_rand_calc_per_node_uses_orig_bd
     my $sp = $bd->add_spatial_output (name => 'sp');
@@ -191,7 +222,7 @@ sub test_rand_structured_richness_same {
             $obs_richness{$group} //= $bd->get_richness_aa ($group) // 0;
             $rand_richness{$group}  = $rand_bd->get_richness_aa ($group) // 0;
         }
-        is \%rand_richness, \%obs_richness, "Richness scores match, $rand_function";
+        is \%rand_richness, \%obs_richness, "Richness scores match, $rand_function $log_suffix";
     }
 
     foreach my $rand_bd (@$rand_bd_array) {
@@ -200,10 +231,10 @@ sub test_rand_structured_richness_same {
             $obs_range{$label} //= $bd->get_range (element => $label);
             $rand_range{$label}  = $rand_bd->get_range (element => $label);
         }
-        is \%obs_range, \%rand_range, "Ranges match, $rand_function";
+        is \%obs_range, \%rand_range, "Ranges match, $rand_function $log_suffix";
     }
 
-    return;
+    return $rand_bd_array;
 }