diff --git a/tests/diff3 b/tests/diff3
index a40631b..b591751 100644
--- a/tests/diff3
+++ b/tests/diff3
@@ -3,6 +3,18 @@
 
 . "${srcdir=.}/init.sh"; path_prepend_ ../src
 
+# Some systems lack seq.
+# A limited replacement for seq: handle 1 or 2 args; increment must be 1
+seq()
+{
+  case $# in
+    1) start=1  final=$1;;
+    2) start=$1 final=$2;;
+    *) echo you lose 1>&2; exit 1;;
+  esac
+  awk 'BEGIN{for(i='$start';i<='$final';i++) print i}' < /dev/null
+}
+
 echo a > a || framework_failure_
 echo b > b || framework_failure_
 echo c > c || framework_failure_