diff --git a/mesonbuild/compilers/mixins/clang.py b/mesonbuild/compilers/mixins/clang.py
index 5e109c057..e7d30fc99 100644
--- a/mesonbuild/compilers/mixins/clang.py
+++ b/mesonbuild/compilers/mixins/clang.py
@@ -35,7 +35,7 @@ clang_color_args = {
 }  # type: T.Dict[str, T.List[str]]
 
 clang_optimization_args = {
-    '0': [],
+    '0': ['-O0'],
     'g': ['-Og'],
     '1': ['-O1'],
     '2': ['-O2'],