diff -ru orig/c2rust-ast-exporter-0.18.0/src/CMakeLists.txt c2rust-ast-exporter-0.18.0/src/CMakeLists.txt
--- orig/c2rust-ast-exporter-0.18.0/src/CMakeLists.txt	2006-07-24 03:21:28.000000000 +0200
+++ c2rust-ast-exporter-0.18.0/src/CMakeLists.txt	2024-12-21 12:06:27.056455735 +0100
@@ -24,8 +24,7 @@
 ExternalProject_Add(tinycbor_build
             PREFIX ${TINYCBOR_PREFIX}
             INSTALL_DIR ${CMAKE_BINARY_DIR}
-            GIT_REPOSITORY ${TINYCBOR_REPO}
-            GIT_TAG ${TINYCBOR_TAG}
+            SOURCE_DIR ${TINYCBOR_SOURCE_DIR}
             # the fd redirection here fails when the build run inside Cargo.
             # patch from upstream:
             # https://github.com/intel/tinycbor/commit/6176e0a28d7c5ef3a5e9cbd02521999c412de72c
diff -ru orig/c2rust-ast-exporter-0.18.0/build.rs c2rust-ast-exporter-0.18.0/build.rs
--- orig/c2rust-ast-exporter-0.18.0/build.rs	2024-12-21 19:37:50.004786236 +0100
+++ c2rust-ast-exporter-0.18.0/build.rs	2024-12-21 19:39:20.188478196 +0100
@@ -127,6 +127,7 @@
             // Build libclangAstExporter.a with cmake
             let dst = Config::new("src")
                 // Where to find LLVM/Clang CMake files
+                .define("TINYCBOR_SOURCE_DIR", &env!("GUIX_TINYCBOR_SOURCE_DIR"))
                 .define("LLVM_DIR", &format!("{}/cmake/llvm", llvm_lib_dir))
                 .define("Clang_DIR", &format!("{}/cmake/clang", llvm_lib_dir))
                 // What to build