diff --git a/tools/export/iar/__init__.py b/tools/export/iar/__init__.py
index eea02fc1e1..e32118f4bf 100644
--- a/tools/export/iar/__init__.py
+++ b/tools/export/iar/__init__.py
@@ -114,7 +114,7 @@ class IAR(Exporter):
         template = ["--vla", "--no_static_destruction"]
         # Flag invalid if set in template
         # Optimizations are also set in template
-        invalid_flag = lambda x: x in template or re.match("-O(\d|time|n)", x)
+        invalid_flag = lambda x: x in template or re.match("-O(\d|time|n|hz?)", x)
         flags['c_flags'] = [flag for flag in c_flags if not invalid_flag(flag)]
 
         try: