diff --git a/src/lib/mappings.ml b/src/lib/mappings.ml
index e72dd9d9f..a2c27f474 100644
--- a/src/lib/mappings.ml
+++ b/src/lib/mappings.ml
@@ -198,9 +198,10 @@ let name_gen prefix =
 
 (* Take a arm like "<pat> => <exp>" and turn it into "<pat> => Some(<exp>)" *)
 let some_arm = function
-  | Pat_aux (Pat_exp (pat, exp), annot) -> Pat_aux (Pat_exp (pat, mk_exp (E_app (mk_id "Some", [exp]))), annot)
-  | Pat_aux (Pat_when (pat, guard, exp), annot) ->
-      Pat_aux (Pat_when (pat, guard, mk_exp (E_app (mk_id "Some", [exp]))), annot)
+  | Pat_aux (Pat_exp (pat, exp), ((l, _) as annot)) ->
+      Pat_aux (Pat_exp (pat, mk_exp ~loc:l (E_app (mk_id "Some", [exp]))), annot)
+  | Pat_aux (Pat_when (pat, guard, exp), ((l, _) as annot)) ->
+      Pat_aux (Pat_when (pat, guard, mk_exp ~loc:l (E_app (mk_id "Some", [exp]))), annot)
 
 let wildcard_none = mk_pexp (Pat_exp (mk_pat P_wild, mk_exp (E_app (mk_id "None", [mk_lit_exp L_unit]))))
 
diff --git a/test/sailcov/nested_mapping1.expect b/test/sailcov/nested_mapping1.expect
new file mode 100644
index 000000000..f910e665f
--- /dev/null
+++ b/test/sailcov/nested_mapping1.expect
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>nested_mapping1</title></head>
+<body>
+<h1>nested_mapping1.sail (2/5) 40%</h1>
+<code style="display: block">
+default&nbsp;Order&nbsp;dec<br>
+$include&nbsp;&lt;prelude.sail&gt;<br>
+<br>
+union&nbsp;ast&nbsp;=&nbsp;{<br>
+&nbsp;&nbsp;B&nbsp;:&nbsp;(bool),<br>
+&nbsp;&nbsp;Z&nbsp;:&nbsp;unit<br>
+}<br>
+<br>
+mapping&nbsp;bool_not_bits&nbsp;:&nbsp;bool&nbsp;&lt;-&gt;&nbsp;bits(1)&nbsp;=&nbsp;{<br>
+&nbsp;&nbsp;<span style="background-color: hsl(0, 85%, 80%)">true</span>&nbsp;&nbsp;&nbsp;&lt;-&gt;&nbsp;0b0,<br>
+&nbsp;&nbsp;<span style="background-color: hsl(0, 85%, 80%)">false</span>&nbsp;&nbsp;&lt;-&gt;&nbsp;0b1<br>
+}<br>
+<br>
+mapping&nbsp;encdec&nbsp;&nbsp;:&nbsp;bits(2)&nbsp;&lt;-&gt;&nbsp;&nbsp;ast&nbsp;=&nbsp;{<br>
+&nbsp;&nbsp;<span style="background-color: hsl(120, 85%, 80%)">0b00</span>&nbsp;&lt;-&gt;&nbsp;Z(),<br>
+&nbsp;&nbsp;<span style="background-color: hsl(0, 85%, 80%)">0b1&nbsp;@&nbsp;bool_not_bits(s)</span>&nbsp;&lt;-&gt;&nbsp;B(s)<br>
+}<br>
+<br>
+val&nbsp;main&nbsp;:&nbsp;unit&nbsp;-&gt;&nbsp;unit<br>
+function&nbsp;main()&nbsp;=&nbsp;<span style="background-color: hsl(120, 85%, 80%)">{<br>
+&nbsp;&nbsp;&nbsp;&nbsp;let&nbsp;_&nbsp;=&nbsp;encdec(0b00)<br>
+}</span><br>
+</code>
+</body>
+</html>
\ No newline at end of file
diff --git a/test/sailcov/nested_mapping1.sail b/test/sailcov/nested_mapping1.sail
new file mode 100644
index 000000000..bbd28bb18
--- /dev/null
+++ b/test/sailcov/nested_mapping1.sail
@@ -0,0 +1,22 @@
+default Order dec
+$include <prelude.sail>
+
+union ast = {
+  B : (bool),
+  Z : unit
+}
+
+mapping bool_not_bits : bool <-> bits(1) = {
+  true   <-> 0b0,
+  false  <-> 0b1
+}
+
+mapping encdec  : bits(2) <->  ast = {
+  0b00 <-> Z(),
+  0b1 @ bool_not_bits(s) <-> B(s)
+}
+
+val main : unit -> unit
+function main() = {
+    let _ = encdec(0b00)
+}
\ No newline at end of file
