diff --git a/src/basic/log.h b/src/basic/log.h
index 3bec4131a79..7218b4bf718 100644
--- a/src/basic/log.h
+++ b/src/basic/log.h
@@ -31,10 +31,10 @@ typedef enum LogTarget{
  * used a regular log level. */
 #define LOG_NULL (LOG_EMERG - 1)
 
-/* Note to readers: << and >> have lower precedence than & and | */
+/* Note to readers: << and >> have lower precedence (are evaluated earlier) than & and | */
 #define SYNTHETIC_ERRNO(num)                (1 << 30 | (num))
 #define IS_SYNTHETIC_ERRNO(val)             ((val) >> 30 & 1)
-#define ERRNO_VALUE(val)                    (abs(val) & 255)
+#define ERRNO_VALUE(val)                    (abs(val) & ~(1 << 30))
 
 /* The callback function to be invoked when syntax warnings are seen
  * in the unit files. */