--- a/config/rules.mk
+++ b/config/rules.mk
@@ -903,29 +903,28 @@ rust_unlock_unstable += RUSTC_BOOTSTRAP=
 endif
 
 ifdef MOZ_USING_SCCACHE
 sccache_wrap := RUSTC_WRAPPER='$(CCACHE)'
 endif
 
 # XXX hack to work around dsymutil failing on cross-OSX builds (bug 1380381)
 ifeq ($(HOST_OS_ARCH)-$(OS_ARCH),Linux-Darwin)
-rust_debug_info=1
+default_rustflags += -C debuginfo=1
 else
-rust_debug_info=2
+default_rustflags += -C debuginfo=2
 endif
 
 # We use the + prefix to pass down the jobserver fds to cargo, but we
 # don't use the prefix when make -n is used, so that cargo doesn't run
 # in that case)
 define RUN_CARGO
 $(if $(findstring n,$(filter-out --%, $(MAKEFLAGS))),,+)env $(environment_cleaner) $(rust_unlock_unstable) $(rustflags_override) $(sccache_wrap) \
 	CARGO_TARGET_DIR=$(CARGO_TARGET_DIR) \
 	RUSTC=$(RUSTC) \
-	RUSTFLAGS='-C debuginfo=$(rust_debug_info)' \
 	MOZ_SRC=$(topsrcdir) \
 	MOZ_DIST=$(ABS_DIST) \
 	LIBCLANG_PATH="$(MOZ_LIBCLANG_PATH)" \
 	CLANG_PATH="$(MOZ_CLANG_PATH)" \
 	PKG_CONFIG_ALLOW_CROSS=1 \
 	RUST_BACKTRACE=1 \
 	MOZ_TOPOBJDIR=$(topobjdir) \
 	$(2) \