diff --git a/glnx-macros.h b/glnx-macros.h
index 1d4e1753e0a11bfbb433d479cfeb3fb2edcad0bd..6d8aca93f8a36b49e378c59bc374e169e0991c71 100644
--- a/glnx-macros.h
+++ b/glnx-macros.h
@@ -38,7 +38,7 @@ G_BEGIN_DECLS
         ({                                                              \
                 const char *_appendees_[] = { a, __VA_ARGS__ };         \
                 char *_d_, *_p_;                                        \
-                int _len_ = 0;                                          \
+                size_t _len_ = 0;                                       \
                 unsigned _i_;                                           \
                 for (_i_ = 0; _i_ < G_N_ELEMENTS(_appendees_) && _appendees_[_i_]; _i_++) \
                         _len_ += strlen(_appendees_[_i_]);              \