@@ -309,7 +309,11 @@ add_custom_target("index-cpp-rules" ALL DEPENDS ${CMAKE_BINARY_DIR}/rules_index/
 set(rust_rules_index_outputs ${CMAKE_BINARY_DIR}/rules_index/index_unsafe.json ${CMAKE_BINARY_DIR}/rules_index/index_refcount.json)
 add_custom_command(
   OUTPUT ${rust_rules_index_outputs}
-  COMMAND ${PREPROCESSOR_BIN} --merge ${CMAKE_BINARY_DIR}/rules_index ${RULES_IR_DIR}
+  COMMAND ${CARGO_ENV_RULE_PREPROCESSOR}
+          RUSTUP_TOOLCHAIN=${RUST_NIGHTLY_VERSION}
+          LD_LIBRARY_PATH=${NIGHTLY_SYSROOT}/lib
+          DYLD_LIBRARY_PATH=${NIGHTLY_SYSROOT}/lib
+          ${PREPROCESSOR_BIN} --merge ${CMAKE_BINARY_DIR}/rules_index ${RULES_IR_DIR}
   DEPENDS ${rust_rules_ir_outputs} ${PREPROCESSOR_BIN}
   VERBATIM
 )