diff --git a/testing/support.py b/testing/support.py
index 063e52c..24c6148 100644
--- a/testing/support.py
+++ b/testing/support.py
@@ -116,7 +116,8 @@ else:
         # assume a standard gcc
         extra_compile_args = ['-Werror', '-Wall', '-Wextra', '-Wconversion',
                               '-Wno-unused-parameter',
-                              '-Wno-unreachable-code']
+                              '-Wno-unreachable-code',
+                              '-Wno-error=sign-conversion']
 
 is_musl = False
 if sys.platform == 'linux':