diff --git a/python/setup.py b/python/setup.py
index 14de590..aaba434 100644
--- a/python/setup.py
+++ b/python/setup.py
@@ -94,6 +94,7 @@ pytrexio_module = Extension('pytrexio._pytrexio',
                             include_dirs = [h5_cflags, srcpath, numpy_includedir],
                             libraries = ['hdf5', 'hdf5_hl'],
                             extra_compile_args = [
+                                '-std=c99',
                                 '-Wno-discarded-qualifiers',
                                 '-Wno-unused-variable',
                                 '-Wno-unused-but-set-variable'