diff --git a/src/psl.c b/src/psl.c
index 283204c..c80edec 100644
--- a/src/psl.c
+++ b/src/psl.c
@@ -33,15 +33,15 @@
 #endif
 
 #if defined(__GNUC__) && defined(__GNUC_MINOR__)
-#       define _GCC_VERSION_AT_LEAST(major, minor) ((__GNUC__ > (major)) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
+#       define GCC_VERSION_AT_LEAST(major, minor) ((__GNUC__ > (major)) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
 #else
-#       define _GCC_VERSION_AT_LEAST(major, minor) 0
+#       define GCC_VERSION_AT_LEAST(major, minor) 0
 #endif
 
-#if _GCC_VERSION_AT_LEAST(2,95)
-#  define _UNUSED __attribute__ ((unused))
+#if GCC_VERSION_AT_LEAST(2,95)
+#  define PSL_UNUSED __attribute__ ((unused))
 #else
-#  define _UNUSED
+#  define PSL_UNUSED
 #endif
 
 #include <sys/types.h>
@@ -1686,7 +1686,7 @@ void psl_free_string(char *str)
  *
  * Since: 0.4
  */
-psl_error_t psl_str_to_utf8lower(const char *str, const char *encoding _UNUSED, const char *locale _UNUSED, char **lower)
+psl_error_t psl_str_to_utf8lower(const char *str, const char *encoding PSL_UNUSED, const char *locale PSL_UNUSED, char **lower)
 {
 	int ret = PSL_ERR_INVALID_ARG;