diff --git a/tsl/src/nodes/gapfill/gapfill_plan.c b/tsl/src/nodes/gapfill/gapfill_plan.c
index 4159418be..549d4d499 100644
--- a/tsl/src/nodes/gapfill/gapfill_plan.c
+++ b/tsl/src/nodes/gapfill/gapfill_plan.c
@@ -199,7 +199,8 @@ static CustomPathMethods gapfill_path_methods = {
 };
 
 static bool
-gapfill_expression_walker(Expr *node, bool (*walker)(), gapfill_walker_context *context)
+gapfill_expression_walker(Expr *node, bool (*walker)(Node *, gapfill_walker_context *),
+						  gapfill_walker_context *context)
 {
 	context->count = 0;
 	context->call.node = NULL;