diff --git a/src/libnm-glib-aux/nm-hash-utils.h b/src/libnm-glib-aux/nm-hash-utils.h
index 0105b542af..19092994aa 100644
--- a/src/libnm-glib-aux/nm-hash-utils.h
+++ b/src/libnm-glib-aux/nm-hash-utils.h
@@ -416,6 +416,9 @@ nm_hash_obfuscate_ptr(guint static_seed, gconstpointer val)
  * values in a global context. */
 #define NM_HASH_OBFUSCATE_PTR(ptr) (nm_hash_obfuscate_ptr(1678382159u, ptr))
 
+/* NM_HASH_OBFUSCATE_PTR_STR needs a buffer of at least this many bytes. */
+#define NM_HASH_OBFUSCATE_PTR_STR_BUF_SIZE 19
+
 #define NM_HASH_OBFUSCATE_PTR_STR(ptr, buf)                                                        \
     ({                                                                                             \
         gconstpointer _ptr = (ptr);                                                                \