diff --git a/libcob/ChangeLog b/libcob/ChangeLog
index 00cd916fe..1d10aab1e 100644
--- a/libcob/ChangeLog
+++ b/libcob/ChangeLog
@@ -1,4 +1,11 @@
 
+2024-07-09  Boris Eng <boris.eng@ocamlpro.com>
+
+	* fileio.c (bdb_bt_compare, indexed_open): handle BDB keys of different
+	  length with a flag USE_BDB_KEYDIFF (passed with preparser flag CPPFLAGS)
+	* common.c (cob_cmp_strings), coblocal.h (cob_cmp_strings):
+	  extracted from (cob_cmp_alnum)
+
 2024-05-15  Simon Sobisch <simonsobisch@gnu.org>
 
 	* profiling.c: fix compile warnings
diff --git a/libcob/coblocal.h b/libcob/coblocal.h
index 46dfcc576..ebbcd023b 100644
--- a/libcob/coblocal.h
+++ b/libcob/coblocal.h
@@ -494,6 +494,9 @@ COB_HIDDEN const char	*cob_get_last_exception_name	(void);
 COB_HIDDEN void		cob_parameter_check	(const char *, const int);
 COB_HIDDEN char*        cob_get_strerror (void);
 
+COB_HIDDEN int		cob_cmp_strings (unsigned char*, unsigned char*,
+						 size_t, size_t, const unsigned char*);
+
 enum cob_case_modifier {
 	CCM_NONE,
 	CCM_LOWER,
diff --git a/libcob/common.c b/libcob/common.c
index 427995006..f528c763c 100644
--- a/libcob/common.c
+++ b/libcob/common.c
@@ -1975,16 +1975,14 @@ cob_cmp_all (cob_field *f1, cob_field *f2)
 	return ret;
 }
 
-/* compare content of field 'f1' to content of 'f2', space padded,
-   using the optional collating sequence of the program */
-static int
-cob_cmp_alnum (cob_field *f1, cob_field *f2)
+/* compare string 'data1' to string 'data2', of size 'size1' and 'size2'
+   respectively, space padded, using a given collating sequence */
+int
+cob_cmp_strings (
+	unsigned char* data1, unsigned char* data2,
+	size_t size1, size_t size2,
+	const unsigned char *col)
 {
-	const unsigned char	*col = COB_MODULE_PTR->collating_sequence;
-	const unsigned char	*data1 = COB_FIELD_DATA (f1);
-	const unsigned char	*data2 = COB_FIELD_DATA (f2);
-	const size_t		size1 = COB_FIELD_SIZE (f1);
-	const size_t		size2 = COB_FIELD_SIZE (f2);	
 	const size_t	min = (size1 < size2) ? size1 : size2;
 	int		ret;
 
@@ -2025,6 +2023,20 @@ cob_cmp_alnum (cob_field *f1, cob_field *f2)
 	return 0;
 }
 
+/* compare content of field 'f1' to content of 'f2', space padded,
+   using the optional collating sequence of the program */
+static int
+cob_cmp_alnum (cob_field *f1, cob_field *f2)
+{
+	const unsigned char	*col = COB_MODULE_PTR->collating_sequence;
+	const unsigned char	*data1 = COB_FIELD_DATA (f1);
+	const unsigned char	*data2 = COB_FIELD_DATA (f2);
+	const size_t		size1 = COB_FIELD_SIZE (f1);
+	const size_t		size2 = COB_FIELD_SIZE (f2);	
+	return cob_cmp_strings ((unsigned char *)data1, (unsigned char *)data2,
+		size1, size2, col);
+}
+
 /* comparision of all key fields for SORT (without explicit collation)
    in records pointed to by 'data1' and 'data2' */
 static int
diff --git a/libcob/fileio.c b/libcob/fileio.c
index ec8dcb88e..1ec33c55e 100644
--- a/libcob/fileio.c
+++ b/libcob/fileio.c
@@ -920,19 +920,24 @@ bdb_bt_compare (DB *db, const DBT *k1, const DBT *k2
 {
 	const unsigned char *col = (unsigned char *)DBT_GET_APP_DATA (k1);
 	COB_UNUSED (db);
-
+#ifdef USE_BDB_KEYDIFF /* flag passed with CPPFLAGS */
+	return cob_cmp_strings (k1->data, k2->data, (size_t)k1->size, (size_t)k2->size, col);
+#else
 	/* LCOV_EXCL_START */
 	if (col == NULL) {
 		cob_runtime_error ("bdb_bt_compare was set but no collating sequence was stored in DBT");
+		cob_hard_failure ();
 	}
 	if (k1->size != k2->size) {
 		cob_runtime_error ("bdb_bt_compare was given keys of different length");
+		cob_hard_failure ();
 	}
 	/* LCOV_EXCL_STOP */
 #if DB_VERSION_MAJOR >= 6
 	locp = NULL;	/* docs: must be set to NULL or corruption can occur ... */
 #endif
 	return indexed_key_compare (k1->data, k2->data, k2->size, col);
+#endif /* USE_BDB_KEYDIFF */
 }
 
 #endif	/* WITH_DB */
@@ -4671,9 +4676,14 @@ indexed_open (cob_file *f, char *filename,
 				if (f->keys[i].tf_duplicates) {
 					p->db[i]->set_flags (p->db[i], DB_DUP);
 				}
+				/* TODO: add national compare function later */
+#ifdef USE_BDB_KEYDIFF
+				p->db[i]->set_bt_compare(p->db[i], bdb_bt_compare);
+#else
 				if (f->keys[i].collating_sequence) {
 					p->db[i]->set_bt_compare(p->db[i], bdb_bt_compare);
 				}
+#endif
 			}
 		} else {
 			handle_created = 0;