diff --git a/S15-nfg/concatenation.t b/S15-nfg/concatenation.t
new file mode 100644
index 0000000000..1d3c9aa3aa
--- /dev/null
+++ b/S15-nfg/concatenation.t
@@ -0,0 +1,25 @@
+use Test;
+
+plan 8;
+
+my $a = "\x0044";
+my $b = "\x0307";
+my $c = "\x0323";
+
+{
+    my $ab = $a ~ $b;
+    my $ac = $a ~ $c;
+    my $abc = $a ~ $b ~ $c;
+    my $acb = $a ~ $c ~ $b;
+    
+    is $ab.chars, 1, 'Base + combiner is 1 grapheme (1)';
+    is $ac.chars, 1, 'Base + combiner is 1 grapheme (2)';
+    is $abc.chars, 1, 'Base + 2 combiners is 1 grapheme (1)';
+    is $acb.chars, 1, 'Base + 2 combiners is 1 grapheme (2)';
+    is $abc, $acb, 'Order of combiners concatenated does not affect equality';
+}
+
+# 3 bases joined with marks is 2 composed/synthetic followed by base
+is ($a, $a, $a).join($b).chars, 3, 'join respects NFG (1)';
+is ($a, $a, $a).join($c).chars, 3, 'join respects NFG (2)';
+is ($a, $a, $a).join($b ~ $c).chars, 3, 'join respects NFG (3)';