diff --git a/bazel/emscripten_toolchain/crosstool.bzl b/bazel/emscripten_toolchain/crosstool.bzl
index 069ea70..b4883ea 100644
--- a/bazel/emscripten_toolchain/crosstool.bzl
+++ b/bazel/emscripten_toolchain/crosstool.bzl
@@ -572,9 +572,10 @@ def _impl(ctx):
         flag_set(
             actions = all_compile_actions +
                       all_link_actions,
-            flags = ["-O3"],
+            flags = ["-O2"],
             features = ["opt"],
         ),
+
         # Users can override opt-level with semantic names...
         flag_set(
             actions = all_compile_actions +
@@ -598,7 +599,7 @@ def _impl(ctx):
         flag_set(
             actions = all_compile_actions +
                       all_link_actions,
-            flags = ["-O2"],
+            flags = ["-O0"],
             features = ["fastbuild"],
         ),