diff --git a/Makefile b/Makefile
index 5d29375a7c1..04bac32dc77 100644
--- a/Makefile
+++ b/Makefile
@@ -129,7 +129,7 @@ PKG_UPDATE_OPTIONS =
 PLT_SETUP_OPTIONS =
 
 # Catalog for package sources:
-SRC_CATALOG = https://download.racket-lang.org/releases/8.6/catalog
+SRC_CATALOG = "https://download.racket-lang.org/releases/8.6/catalog/"
 
 # Built-in catalog for package sources (not meant to be configured):
 DEFAULT_SRC_CATALOG = https://pkgs.racket-lang.org