diff --git a/build-aux/flatpak/org.gnome.Loupe.Devel.json b/build-aux/flatpak/org.gnome.Loupe.Devel.json
index edaac4f..16c5ce7 100644
--- a/build-aux/flatpak/org.gnome.Loupe.Devel.json
+++ b/build-aux/flatpak/org.gnome.Loupe.Devel.json
@@ -27,6 +27,7 @@
             "--share=network"
         ],
         "env" : {
+            "CARGO_REGISTRIES_CRATES_IO_PROTOCOL" : "sparse",
             "CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER" : "clang",
             "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER" : "clang",
             "CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS" : "-C link-arg=-fuse-ld=/usr/lib/sdk/rust-stable/bin/mold",