diff --git a/lib/isc/base64.c b/lib/isc/base64.c
index ba4ee7148f..3b2d19af70 100644
--- a/lib/isc/base64.c
+++ b/lib/isc/base64.c
@@ -179,7 +179,7 @@ isc_base64_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length) {
 	isc_token_t token;
 	bool eol;
 
-	REQUIRE(length >= -2);
+	REQUIRE(length >= isc_one_or_more);
 
 	base64_decode_init(&ctx, length, target);
 
@@ -207,7 +207,7 @@ isc_base64_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length) {
 		isc_lex_ungettoken(lexer, &token);
 	}
 	RETERR(base64_decode_finish(&ctx));
-	if (length == -2 && before == after) {
+	if (length == isc_one_or_more && before == after) {
 		return ISC_R_UNEXPECTEDEND;
 	}
 	return ISC_R_SUCCESS;
@@ -217,7 +217,7 @@ isc_result_t
 isc_base64_decodestring(const char *cstr, isc_buffer_t *target) {
 	base64_decode_ctx_t ctx;
 
-	base64_decode_init(&ctx, -1, target);
+	base64_decode_init(&ctx, isc_zero_or_more, target);
 	for (;;) {
 		int c = *cstr++;
 		if (c == '\0') {
diff --git a/lib/isc/hex.c b/lib/isc/hex.c
index 7f63df7aa6..e063d2fc2b 100644
--- a/lib/isc/hex.c
+++ b/lib/isc/hex.c
@@ -128,7 +128,7 @@ isc_hex_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length) {
 	isc_token_t token;
 	bool eol;
 
-	REQUIRE(length >= -2);
+	REQUIRE(length >= isc_one_or_more);
 
 	isc_hex_decodeinit(&ctx, length, target);
 
@@ -156,7 +156,7 @@ isc_hex_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length) {
 		isc_lex_ungettoken(lexer, &token);
 	}
 	RETERR(isc_hex_decodefinish(&ctx));
-	if (length == -2 && before == after) {
+	if (length == isc_one_or_more && before == after) {
 		return ISC_R_UNEXPECTEDEND;
 	}
 	return ISC_R_SUCCESS;
@@ -166,7 +166,7 @@ isc_result_t
 isc_hex_decodestring(const char *cstr, isc_buffer_t *target) {
 	isc_hex_decodectx_t ctx;
 
-	isc_hex_decodeinit(&ctx, -1, target);
+	isc_hex_decodeinit(&ctx, isc_zero_or_more, target);
 	for (;;) {
 		int c = *cstr++;
 		if (c == '\0') {
diff --git a/lib/isc/include/isc/base64.h b/lib/isc/include/isc/base64.h
index 8eba7826ab..a8e93bb650 100644
--- a/lib/isc/include/isc/base64.h
+++ b/lib/isc/include/isc/base64.h
@@ -72,8 +72,11 @@ isc_base64_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length);
  * `target`. If 'length' is non-negative, it is the expected number of
  * encoded octets to convert.
  *
- * If 'length' is -1 then 0 or more encoded octets are expected.
- * If 'length' is -2 then 1 or more encoded octets are expected.
+ * If 'length' is isc_zero_or_more then 0 or more encoded octets are
+ * expected.
+ *
+ * If 'length' is isc_one_or_more then 1 or more encoded octets are
+ * expected.
  *
  * Returns:
  *\li	#ISC_R_BADBASE64 -- invalid base64 encoding.
diff --git a/lib/isc/include/isc/hex.h b/lib/isc/include/isc/hex.h
index 76675c7fad..ebe042cb74 100644
--- a/lib/isc/include/isc/hex.h
+++ b/lib/isc/include/isc/hex.h
@@ -143,8 +143,11 @@ isc_hex_tobuffer(isc_lex_t *lexer, isc_buffer_t *target, int length);
  * `target`. If 'length' is non-negative, it is the expected number of
  * encoded octets to convert.
  *
- * If 'length' is -1 then 0 or more encoded octets are expected.
- * If 'length' is -2 then 1 or more encoded octets are expected.
+ * If 'length' is isc_zero_or_more then 0 or more encoded octets are
+ * expected.
+ *
+ * If 'length' is isc_one_or_more then 1 or more encoded octets are
+ * expected.
  *
  * Returns:
  *\li	#ISC_R_BADHEX -- invalid hex encoding
diff --git a/lib/isc/include/isc/types.h b/lib/isc/include/isc/types.h
index 3ab5f5d771..74ba9ff946 100644
--- a/lib/isc/include/isc/types.h
+++ b/lib/isc/include/isc/types.h
@@ -80,6 +80,12 @@ typedef struct isc_nm_http_endpoints isc_nm_http_endpoints_t;
 /*%< HTTP endpoints set */
 #endif /* HAVE_LIBNGHTTP2 */
 
+/*% Used by isc_base64 and isc_hex for expected lower bound */
+enum {
+	isc_zero_or_more = -1,
+	isc_one_or_more = -2,
+};
+
 /*% Statistics formats (text file or XML) */
 typedef enum {
 	isc_statsformat_file,