diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c
index 72747be9e2..0b5b81c7f2 100644
--- a/src/backend/parser/parse_coerce.c
+++ b/src/backend/parser/parse_coerce.c
@@ -661,10 +661,8 @@ can_coerce_type(int nargs, const Oid *input_typeids, const Oid *target_typeids,
  * Create an expression tree to represent coercion to a domain type.
  *
  * 'arg': input expression
- * 'baseTypeId': base type of domain, if known (pass InvalidOid if caller
- *		has not bothered to look this up)
- * 'baseTypeMod': base type typmod of domain, if known (pass -1 if caller
- *		has not bothered to look this up)
+ * 'baseTypeId': base type of domain
+ * 'baseTypeMod': base type typmod of domain
  * 'typeId': target type to coerce to
  * 'ccontext': context indicator to control coercions
  * 'cformat': coercion display format
@@ -680,9 +678,8 @@ coerce_to_domain(Node *arg, Oid baseTypeId, int32 baseTypeMod, Oid typeId,
 {
 	CoerceToDomain *result;
 
-	/* Get the base type if it hasn't been supplied */
-	if (baseTypeId == InvalidOid)
-		baseTypeId = getBaseTypeAndTypmod(typeId, &baseTypeMod);
+	/* We now require the caller to supply correct baseTypeId/baseTypeMod */
+	Assert(OidIsValid(baseTypeId));
 
 	/* If it isn't a domain, return the node as it was passed in */
 	if (baseTypeId == typeId)