diff --git a/CHANGES b/CHANGES
index 3923c6bc68..86bdfaa330 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+3668.	[bug]		Fix cast in lex.c which could see 0xff treated as eof.
+			[RT #34993]
+
 3667.	[func]		dig: add support to keep the TCP socket open between
 			successive queries (+[no]keepopen).  [RT #34918]
 
diff --git a/lib/isc/lex.c b/lib/isc/lex.c
index 8749ed0b0b..64d54ec613 100644
--- a/lib/isc/lex.c
+++ b/lib/isc/lex.c
@@ -445,7 +445,7 @@ isc_lex_gettoken(isc_lex_t *lex, unsigned int options, isc_token_t *tokenp) {
 					c = EOF;
 					source->at_eof = ISC_TRUE;
 				} else {
-					c = *((char *)buffer->base +
+					c = *((unsigned char *)buffer->base +
 					      buffer->current);
 					buffer->current++;
 				}
diff --git a/lib/isc/tests/Makefile.in b/lib/isc/tests/Makefile.in
index 4d4328942f..daedea27f3 100644
--- a/lib/isc/tests/Makefile.in
+++ b/lib/isc/tests/Makefile.in
@@ -36,12 +36,14 @@ LIBS =		@LIBS@ @ATFLIBS@
 
 OBJS =		isctest.@O@
 SRCS =		isctest.c taskpool_test.c socket_test.c hash_test.c \
+		lex_test.c \
 		sockaddr_test.c symtab_test.c task_test.c queue_test.c \
 		parse_test.c pool_test.c regex_test.c socket_test.c \
 		safe_test.c
 
 SUBDIRS =
 TARGETS =	taskpool_test@EXEEXT@ socket_test@EXEEXT@ hash_test@EXEEXT@ \
+		lex_test@EXEEXT@ \
 		sockaddr_test@EXEEXT@ symtab_test@EXEEXT@ task_test@EXEEXT@ \
 		queue_test@EXEEXT@ parse_test@EXEEXT@ pool_test@EXEEXT@ \
 		regex_test@EXEEXT@ socket_test@EXEEXT@ safe_test@EXEEXT@
@@ -64,6 +66,10 @@ hash_test@EXEEXT@: hash_test.@O@ ${ISCDEPLIBS}
 	${LIBTOOL_MODE_LINK} ${PURIFY} ${CC} ${CFLAGS} ${LDFLAGS} -o $@ \
 			hash_test.@O@ ${ISCLIBS} ${LIBS}
 
+lex_test@EXEEXT@: lex_test.@O@ ${ISCDEPLIBS}
+	${LIBTOOL_MODE_LINK} ${PURIFY} ${CC} ${CFLAGS} ${LDFLAGS} -o $@ \
+			lex_test.@O@ ${ISCLIBS} ${LIBS}
+
 queue_test@EXEEXT@: queue_test.@O@ isctest.@O@ ${ISCDEPLIBS}
 	${LIBTOOL_MODE_LINK} ${PURIFY} ${CC} ${CFLAGS} ${LDFLAGS} -o $@ \
 			queue_test.@O@ isctest.@O@ ${ISCLIBS} ${LIBS}
diff --git a/lib/isc/tests/lex_test.c b/lib/isc/tests/lex_test.c
new file mode 100644
index 0000000000..7e96bb2283
--- /dev/null
+++ b/lib/isc/tests/lex_test.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2013  Internet Systems Consortium, Inc. ("ISC")
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+ * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <config.h>
+
+#include <atf-c.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <isc/buffer.h>
+#include <isc/lex.h>
+#include <isc/mem.h>
+#include <isc/util.h>
+
+ATF_TC(lex);
+ATF_TC_HEAD(lex, tc) {
+	atf_tc_set_md_var(tc, "descr", "check handling of 0xff");
+}
+ATF_TC_BODY(lex, tc) {
+	isc_mem_t *mctx = NULL;
+	isc_result_t result;
+	isc_lex_t *lex = NULL;
+	isc_buffer_t death_buf;
+	isc_token_t token;
+
+	unsigned char death[] = { EOF, 'A' };
+
+	UNUSED(tc);
+
+	result = isc_mem_create(0, 0, &mctx);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+
+	result = isc_lex_create(mctx, 1024, &lex);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+
+	isc_buffer_init(&death_buf, &death[0], sizeof(death));
+	isc_buffer_add(&death_buf, sizeof(death));
+
+	result = isc_lex_openbuffer(lex, &death_buf);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+
+	result = isc_lex_gettoken(lex, 0, &token);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+}
+
+/*
+ * Main
+ */
+ATF_TP_ADD_TCS(tp) {
+	ATF_TP_ADD_TC(tp, lex);
+	return (atf_no_error());
+}
+