diff --git a/CHANGES.md b/CHANGES.md
index 4b45fa5bf9..58847f9222 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -10,6 +10,8 @@ unreleased
     - Fix bugs on signature help about labelled and optional parameters (#2032)
     - Add `-end-position` parameter for `enclosing` (#2029)
     - Signature help should appear even if the 'in' is not written (#2036)
+  + merlin binary
+    - Define PATH_MAX to 4096 if undefined (eg. hurd) (#2039)
   + tests
     - Add a reproduction case for #1214, the issue has been resolved before (#2022)
     - Add reproduction case for #1763 but it is not failing anymore (#2021)
diff --git a/src/frontend/ocamlmerlin/ocamlmerlin.c b/src/frontend/ocamlmerlin/ocamlmerlin.c
index 2046839902..81ecd159a6 100644
--- a/src/frontend/ocamlmerlin/ocamlmerlin.c
+++ b/src/frontend/ocamlmerlin/ocamlmerlin.c
@@ -132,6 +132,11 @@ static void failwith(const char *msg)
   exit(EXIT_FAILURE);
 }
 
+#ifndef PATH_MAX
+/* PATH_MAX is undefined on e.g. Hurd */
+#define PATH_MAX 8192
+#endif
+
 #ifdef _WIN32
 #define PATHSZ (MAX_PATH+1)
 #define SOCKSZ (MAX_PATH+1)