--- a/gfx/cairo/cairo/src/moz.build
+++ b/gfx/cairo/cairo/src/moz.build
@@ -217,16 +217,17 @@ if CONFIG['MOZ_TREE_FREETYPE']:
 if CONFIG['GNU_CC'] or CONFIG['CLANG_CL']:
     CFLAGS += [
         '-Wno-enum-compare',
         '-Wno-int-to-pointer-cast',
         '-Wno-sign-compare',
         '-Wno-type-limits',
         '-Wno-missing-field-initializers',
         '-Wno-conversion',
+        '-Wno-unused-but-set-variable',
     ]
 if CONFIG['CLANG_CXX'] or CONFIG['CLANG_CL']:
     CFLAGS += [
         '-Wno-incompatible-pointer-types',
         '-Wno-tautological-compare',
         '-Wno-tautological-constant-out-of-range-compare',
         '-Wno-error=uninitialized',
     ]