diff --git a/src/libsystemd/sd-id128/id128-util.c b/src/libsystemd/sd-id128/id128-util.c
index 7c66d1c2db..c0fae60dc5 100644
--- a/src/libsystemd/sd-id128/id128-util.c
+++ b/src/libsystemd/sd-id128/id128-util.c
@@ -49,8 +49,8 @@ bool id128_is_valid(const char *s) {
                         char c = s[i];
 
                         if (!(c >= '0' && c <= '9') &&
-                            !(c >= 'a' && c <= 'z') &&
-                            !(c >= 'A' && c <= 'Z'))
+                            !(c >= 'a' && c <= 'f') &&
+                            !(c >= 'A' && c <= 'F'))
                                 return false;
                 }
 
@@ -66,8 +66,8 @@ bool id128_is_valid(const char *s) {
                                         return false;
                         } else {
                                 if (!(c >= '0' && c <= '9') &&
-                                    !(c >= 'a' && c <= 'z') &&
-                                    !(c >= 'A' && c <= 'Z'))
+                                    !(c >= 'a' && c <= 'f') &&
+                                    !(c >= 'A' && c <= 'F'))
                                         return false;
                         }
                 }