1 files changed, 2 insertions, 0 deletions
diff --git a/emcc b/emcc
index ff443389..fc580d0f 100755
--- a/emcc
+++ b/emcc
@@ -993,6 +993,8 @@ try:
 
   # Apply effects from settings
   if shared.Settings.ASM_JS:
+    assert opt_level == 2, 'asm.js requires -O2'
+
     if closure:
       print >> sys.stderr, 'emcc: warning: disabling closure because it is not compatible with asm.js code generation'
       closure = False