diff --git a/src/backend/parser/parse_param.c b/src/backend/parser/parse_param.c
index 20abf00..f4381fc 100644
--- a/src/backend/parser/parse_param.c
+++ b/src/backend/parser/parse_param.c
@@ -55,6 +55,9 @@ static Node *variable_paramref_hook(ParseState *pstate, ParamRef *pref);
 static Node *variable_coerce_param_hook(ParseState *pstate, Param *param,
 						   Oid targetTypeId, int32 targetTypeMod,
 						   int location);
+static Node *fixed_coerce_param_hook(ParseState *pstate, Param *param,
+						   Oid targetTypeId, int32 targetTypeMod,
+						   int location);
 static bool check_parameter_resolution_walker(Node *node, ParseState *pstate);
 
 
@@ -71,7 +74,7 @@ parse_fixed_parameters(ParseState *pstate,
 	parstate->numParams = numParams;
 	pstate->p_ref_hook_state = (void *) parstate;
 	pstate->p_paramref_hook = fixed_paramref_hook;
-	/* no need to use p_coerce_param_hook */
+	pstate->p_coerce_param_hook = fixed_coerce_param_hook;
 }
 
 /*
@@ -170,6 +173,43 @@ variable_paramref_hook(ParseState *pstate, ParamRef *pref)
 	return (Node *) param;
 }
 
+static Node *
+fixed_coerce_param_hook(ParseState *pstate, Param *param,
+						Oid targetTypeId, int32 targetTypeMode,
+						int location)
+{
+	if (param->paramkind == PARAM_EXTERN && param->paramtype == UNKNOWNOID)
+	{
+		/*
+		 * Input is a Param of previously undetermined type, and we want to
+		 * update our knowledge of the Param's type.
+		 */
+		FixedParamState *parstate = (FixedParamState *) pstate->p_ref_hook_state;
+		int			paramno = param->paramid;
+		CoerceViaIO *iocoerce;
+
+		if (paramno <= 0 ||		/* shouldn't happen, but... */
+			paramno > parstate->numParams)
+			ereport(ERROR,
+					(errcode(ERRCODE_UNDEFINED_PARAMETER),
+					 errmsg("there is no parameter $%d", paramno),
+					 parser_errposition(pstate, param->location)));
+
+		/* Build a CoerceViaIO node */
+		iocoerce = makeNode(CoerceViaIO);
+		iocoerce->arg = (Expr *) param;
+		iocoerce->resulttype = targetTypeId;
+		iocoerce->coerceformat = COERCE_IMPLICIT_CAST;
+		iocoerce->location = location;
+
+		return (Node *) iocoerce;
+	}
+
+	/* Else signal to proceed with normal coercion */
+	return NULL;
+}
+
+
 /*
  * Coerce a Param to a query-requested datatype, in the varparams case.
  */