diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 3737166..501b0e9 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -1172,6 +1172,16 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 		return true;
 	if (IsA(node, FieldStore))
 		return true;
+	if (IsA(node, CoerceViaIO))
+	{
+		/*
+		 * CoerceViaIO is strict regardless of whether the I/O functions are,
+		 * so just go look at its argument; asking check_functions_in_node is
+		 * useless expense and could deliver the wrong answer.
+		 */
+		return contain_nonstrict_functions_walker((Node *) ((CoerceViaIO *) node)->arg,
+												  context);
+	}
 	if (IsA(node, ArrayCoerceExpr))
 	{
 		/*
@@ -1179,9 +1189,8 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 		 * the per-element expression is; so we should ignore elemexpr and
 		 * recurse only into the arg.
 		 */
-		return expression_tree_walker((Node *) ((ArrayCoerceExpr *) node)->arg,
-									  contain_nonstrict_functions_walker,
-									  context);
+		return contain_nonstrict_functions_walker((Node *) ((ArrayCoerceExpr *) node)->arg,
+												  context);
 	}
 	if (IsA(node, CaseExpr))
 		return true;
diff --git a/src/backend/optimizer/util/predtest.c b/src/backend/optimizer/util/predtest.c
index 01f64ee..179b9aa 100644
--- a/src/backend/optimizer/util/predtest.c
+++ b/src/backend/optimizer/util/predtest.c
@@ -1352,6 +1352,15 @@ clause_is_strict_for(Node *clause, Node *subexpr)
 		return false;
 	}
 
+	/*
+	 * CoerceViaIO is strict (whether or not the I/O functions it calls are).
+	 * This is worth checking mainly because it saves us having to explain to
+	 * users why some type coercions are known strict and others aren't.
+	 */
+	if (IsA(clause, CoerceViaIO))
+		return clause_is_strict_for((Node *) ((CoerceViaIO *) clause)->arg,
+									subexpr);
+
 	return false;
 }