--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -1296,18 +1296,27 @@ def developer_options(value):
 
 
 add_old_configure_assignment('DEVELOPER_OPTIONS', developer_options)
 set_config('DEVELOPER_OPTIONS', developer_options)
 
 # Rust compiler flags
 # ==============================================================
 
-@depends(moz_optimize, debug_rust, '--enable-debug-symbols')
-def rust_compiler_flags(moz_optimize, debug_rust, debug_symbols):
+js_option(env='RUSTC_OPT_LEVEL',
+          nargs=1,
+          help='Rust compiler optimization level (-C opt-level=%s)')
+
+# --enable-release kicks in full optimizations.
+imply_option('RUSTC_OPT_LEVEL', '2', when='--enable-release')
+
+@depends('RUSTC_OPT_LEVEL', debug_rust, '--enable-debug-symbols',
+         moz_optimize)
+def rust_compiler_flags(opt_level_option, debug_rust, debug_symbols,
+                        moz_optimize):
     optimize = moz_optimize.optimize
 
     # Cargo currently supports only two interesting profiles for building:
     # development and release. Those map (roughly) to --enable-debug and
     # --disable-debug in Gecko, respectively.
     #
     # But we'd also like to support an additional axis of control for
     # optimization level. Since Cargo only supports 2 profiles, we're in
@@ -1316,18 +1325,20 @@ def rust_compiler_flags(moz_optimize, de
     # Code here derives various compiler options given other configure options.
     # The options defined here effectively override defaults specified in
     # Cargo.toml files.
 
     opt_level = None
     debug_assertions = None
     debug_info = None
 
-    if not optimize:
-        opt_level = '0'
+    if opt_level_option.origin != 'default':
+        opt_level = opt_level_option[0]
+    else:
+        opt_level = '1' if optimize else '0'
 
     # opt-level=0 implies -C debug-assertions, which may not be desired
     # unless Rust debugging is enabled.
     if opt_level == '0' and not debug_rust:
         debug_assertions = False
 
     if debug_symbols:
         debug_info = '2'