diff --git a/lib/isc/tests/lex_test.c b/lib/isc/tests/lex_test.c
index 059d323bf0..a4b27606e5 100644
--- a/lib/isc/tests/lex_test.c
+++ b/lib/isc/tests/lex_test.c
@@ -29,6 +29,8 @@
 
 #include "isctest.h"
 
+static bool debug = false;
+
 static int
 _setup(void **state) {
 	isc_result_t result;
@@ -119,13 +121,121 @@ lex_setline(void **state) {
 	isc_lex_destroy(&lex);
 }
 
+/*%
+ * keypair is <string>=<qstring>.  This has implications double quotes
+ * in key names.
+ */
+static void
+lex_keypair(void **state) {
+	isc_buffer_t buf;
+	isc_lex_t *lex = NULL;
+	isc_result_t result;
+	isc_token_t token;
+	size_t i;
+
+	struct {
+		const char *text;
+		const char *value;
+		isc_result_t result;
+		isc_tokentype_t type;
+	} tests[] = {
+		{ "", "", ISC_R_SUCCESS, isc_tokentype_eof },
+		{ "1234", "1234", ISC_R_SUCCESS, isc_tokentype_string },
+		{ "1234=", "1234=", ISC_R_SUCCESS, isc_tokentype_vpair },
+		{ "1234=foo", "1234=foo", ISC_R_SUCCESS, isc_tokentype_vpair },
+		{ "1234=\"foo", NULL, ISC_R_UNEXPECTEDEND, 0 },
+		{ "1234=\"foo\"", "1234=foo", ISC_R_SUCCESS,
+		  isc_tokentype_qvpair },
+		{ "key", "key", ISC_R_SUCCESS, isc_tokentype_string },
+		{ "\"key=", "\"key=", ISC_R_SUCCESS, isc_tokentype_vpair },
+		{ "\"key=\"", NULL, ISC_R_UNEXPECTEDEND, 0 },
+		{ "key=\"\"", "key=", ISC_R_SUCCESS, isc_tokentype_qvpair },
+		{ "key=\"a b\"", "key=a b", ISC_R_SUCCESS,
+		  isc_tokentype_qvpair },
+		{ "key=\"a\tb\"", "key=a\tb", ISC_R_SUCCESS,
+		  isc_tokentype_qvpair },
+		/* double quote not immediately after '=' is not special. */
+		{ "key=c\"a b\"", "key=c\"a", ISC_R_SUCCESS,
+		  isc_tokentype_vpair },
+		/* remove special meaning for '=' by escaping */
+		{ "key\\=", "key\\=", ISC_R_SUCCESS, isc_tokentype_string },
+		{ "key\\=\"a\"", "key\\=\"a\"", ISC_R_SUCCESS,
+		  isc_tokentype_string },
+		{ "key\\=\"a \"", "key\\=\"a", ISC_R_SUCCESS,
+		  isc_tokentype_string },
+		/* vpair with a key of 'key\=' (would need to be deescaped) */
+		{ "key\\==", "key\\==", ISC_R_SUCCESS, isc_tokentype_vpair },
+		/* qvpair with a key of 'key\=' (would need to be deescaped) */
+		{ "key\\==\"\"", "key\\==", ISC_R_SUCCESS,
+		  isc_tokentype_qvpair },
+	};
+
+	UNUSED(state);
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		result = isc_lex_create(test_mctx, 1024, &lex);
+		assert_int_equal(result, ISC_R_SUCCESS);
+
+		isc_buffer_constinit(&buf, tests[i].text,
+				     strlen(tests[i].text));
+		isc_buffer_add(&buf, strlen(tests[i].text));
+
+		result = isc_lex_openbuffer(lex, &buf);
+		assert_int_equal(result, ISC_R_SUCCESS);
+
+		result = isc_lex_setsourceline(lex, 100);
+		assert_int_equal(result, ISC_R_SUCCESS);
+
+		memset(&token, 0, sizeof(token));
+		result = isc_lex_getmastertoken(lex, &token,
+						isc_tokentype_qvpair, true);
+		if (debug) {
+			fprintf(stdout, "# '%s' -> result=%s/%s, type=%u/%u\n",
+				tests[i].text, isc_result_toid(result),
+				isc_result_toid(tests[i].result), token.type,
+				tests[i].type);
+		}
+
+		assert_int_equal(result, tests[i].result);
+		if (result == ISC_R_SUCCESS) {
+			switch (token.type) {
+			case isc_tokentype_string:
+			case isc_tokentype_qstring:
+			case isc_tokentype_vpair:
+			case isc_tokentype_qvpair:
+				if (debug) {
+#define AS_STR(x) (x).value.as_textregion.base
+					fprintf(stdout, "# value='%s'\n",
+						AS_STR(token));
+				}
+				assert_int_equal(token.type, tests[i].type);
+				assert_string_equal(AS_STR(token),
+						    tests[i].value);
+				break;
+			default:
+				assert_int_equal(token.type, tests[i].type);
+				break;
+			}
+		}
+
+		isc_lex_destroy(&lex);
+	}
+}
+
 int
-main(void) {
+main(int argc, char *argv[]) {
 	const struct CMUnitTest tests[] = {
 		cmocka_unit_test(lex_0xff),
+		cmocka_unit_test(lex_keypair),
 		cmocka_unit_test(lex_setline),
 	};
 
+	UNUSED(argv);
+
+	if (argc > 1) {
+		debug = true;
+	}
+
 	return (cmocka_run_group_tests(tests, _setup, _teardown));
 }