diff --git a/document/core/exec/instructions.rst b/document/core/exec/instructions.rst
index ab3ef5b0ab..26f845a66e 100644
--- a/document/core/exec/instructions.rst
+++ b/document/core/exec/instructions.rst
@@ -986,7 +986,7 @@ Memory Instructions
 
     a. Let :math:`n` be the integer for which :math:`\bytes_{\iN}(n) = b^\ast`.
 
-    b. Let :math:`c` be the result of computing :math:`\extend\F{\_}\sx_{N,|t|}(n)`.
+    b. Let :math:`c` be the result of computing :math:`\extend^{\sx}_{N,|t|}(n)`.
 
 13. Else:
 
@@ -1009,7 +1009,7 @@ Memory Instructions
    \\[1ex]
    \begin{array}{lcl@{\qquad}l}
    S; F; (\I32.\CONST~i)~(t.\LOAD{N}\K{\_}\sx~\memarg) &\stepto&
-     S; F; (t.\CONST~\extend\F{\_}\sx_{N,|t|}(n))
+     S; F; (t.\CONST~\extend^{\sx}_{N,|t|}(n))
    \end{array}
    \\ \qquad
      \begin{array}[t]{@{}r@{~}l@{}}
diff --git a/test/core/select.wast b/test/core/select.wast
index bfa30636c5..b343bf93cb 100644
--- a/test/core/select.wast
+++ b/test/core/select.wast
@@ -405,6 +405,14 @@
   "type mismatch"
 )
 
+(assert_invalid
+  (module (func $type-num-vs-num (select (i32.const 1) (i64.const 1) (i32.const 1)) (drop)))
+  "type mismatch"
+)
+(assert_invalid
+  (module (func $type-num-vs-num (select (i32.const 1) (f32.const 1.0) (i32.const 1)) (drop)))
+  "type mismatch"
+)
 (assert_invalid
   (module (func $type-num-vs-num (select (i32.const 1) (i64.const 1) (i32.const 1)) (drop)))
   "type mismatch"