diff --git a/src/eccodes_prototypes.h b/src/eccodes_prototypes.h
index 3569a53eb..61f0a4acd 100644
--- a/src/eccodes_prototypes.h
+++ b/src/eccodes_prototypes.h
@@ -1076,7 +1076,7 @@ void grib_math_delete(grib_context* c, grib_math* m);
 grib_math* grib_math_new(grib_context* c, const char* formula, int* err);
 
 /* grib_hash_keys.c */
-const struct grib_keys_hash* grib_keys_hash_get(const char* str, unsigned int len);
+const struct grib_keys_hash* grib_keys_hash_get(register const char *str, register size_t len);
 grib_itrie* grib_hash_keys_new(grib_context* c, int* count);
 void grib_hash_keys_delete(grib_itrie* t);
 int grib_hash_keys_get_id(grib_itrie* t, const char* key);
diff --git a/src/grib_hash_keys.c b/src/grib_hash_keys.c
index c25dc32f8..3f34648aa 100644
--- a/src/grib_hash_keys.c
+++ b/src/grib_hash_keys.c
@@ -1,4 +1,4 @@
-/* C code produced by gperf version 3.0.4 */
+/* ANSI-C code produced by gperf version 3.1 */
 /* Command-line: gperf -l -C -I -t -G -H hash_keys -N grib_keys_hash_get -m 3 ../tests/keys  */
 /* Computed positions: -k'1-16,19-20,23-26,28,$' */
 
@@ -26,7 +26,7 @@
       && ('w' == 119) && ('x' == 120) && ('y' == 121) && ('z' == 122) \
       && ('{' == 123) && ('|' == 124) && ('}' == 125) && ('~' == 126))
 /* The character set is not based on ISO-646.  */
-error "gperf generated tables don't work with this execution character set. Please report a bug to <bug-gnu-gperf@gnu.org>."
+#error "gperf generated tables don't work with this execution character set. Please report a bug to <bug-gperf@gnu.org>."
 #endif
 
 
@@ -49,7 +49,7 @@ inline
 #endif
 #endif
 static unsigned int
-hash_keys (const char *str, unsigned int len)
+hash_keys (register const char *str, register size_t len)
 {
   static const unsigned short asso_values[] =
     {
@@ -80,7 +80,7 @@ hash_keys (const char *str, unsigned int len)
       32423, 32423, 32423, 32423, 32423, 32423, 32423, 32423, 32423, 32423,
       32423, 32423, 32423, 32423, 32423, 32423, 32423, 32423, 32423
     };
-  register int hval = len;
+  register unsigned int hval = len;
 
   switch (hval)
     {
@@ -9396,13 +9396,13 @@ static const struct grib_keys_hash wordlist[] =
   };
 
 const struct grib_keys_hash *
-grib_keys_hash_get (const char *str, unsigned int len)
+grib_keys_hash_get (register const char *str, register size_t len)
 {
   if (len <= MAX_WORD_LENGTH && len >= MIN_WORD_LENGTH)
     {
-      register int key = hash_keys (str, len);
+      register unsigned int key = hash_keys (str, len);
 
-      if (key <= MAX_HASH_VALUE && key >= 0)
+      if (key <= MAX_HASH_VALUE)
         if (len == lengthtable[key])
           {
             register const char *s = wordlist[key].name;
diff --git a/src/make_hash_keys.ksh b/src/make_hash_keys.ksh
index 66a3c88f8..b9210e810 100755
--- a/src/make_hash_keys.ksh
+++ b/src/make_hash_keys.ksh
@@ -1,4 +1,4 @@
-#!/usr/bin/ksh
+#!/bin/sh
 set -xe
 
 cd ../tests
@@ -22,3 +22,4 @@ gperf -l -C -I -t -G -H hash_keys -N grib_keys_hash_get -m 3  ../tests/keys |\
 
 cat grib_itrie_keys.c >> grib_hash_keys.c
 
+echo ALL DONE