--- a/src/third_party/mozjs/SConscript
+++ b/src/third_party/mozjs/SConscript
@@ -145,8 +145,7 @@ sources = [
 ]
 
 if env['TARGET_ARCH'] == 'x86_64' and not env.TargetOSIs('windows'):
-    env.Append(CCFLAGS=['-mavx2'])
-    sources.extend(["extract/mozglue/misc/SIMD_avx2.cpp", "extract/mozglue/misc/SSE.cpp"])
+    sources.extend(["extract/mozglue/misc/SSE.cpp"])
 
 if env.TargetOSIs('windows'):
     sources.extend([
diff --git a/src/third_party/mozjs/extract/mozglue/misc/SIMD.cpp b/src/third_party/mozjs/extract/mozglue/misc/SIMD.cpp
index 3893de57b32..4ea0a657fbb 100644
--- a/src/third_party/mozjs/extract/mozglue/misc/SIMD.cpp
+++ b/src/third_party/mozjs/extract/mozglue/misc/SIMD.cpp
@@ -448,7 +448,7 @@ const char* SIMD::memchr8SSE2(const char* ptr, char value, size_t length) {
 // assertion failure. Accordingly, we just don't allow that to happen. We
 // are not particularly concerned about ensuring that newer 32 bit processors
 // get access to the AVX2 functions exposed here.
-#  if defined(MOZILLA_MAY_SUPPORT_AVX2) && defined(__x86_64__)
+#  if 0
 
 bool SupportsAVX2() { return supports_avx2(); }