diff --git a/lib/isc/include/isc/stdio.h b/lib/isc/include/isc/stdio.h

index 1f44b5a..a3625f9 100644

--- a/lib/isc/include/isc/stdio.h

+++ b/lib/isc/include/isc/stdio.h

@@ -69,6 +69,9 @@ isc_stdio_sync(FILE *f);

  * direct counterpart in the stdio library.

  */

+isc_result_t

+isc_stdio_fgetc(FILE *f, int *ret);

+

 ISC_LANG_ENDDECLS

 #endif /* ISC_STDIO_H */

diff --git a/lib/isc/lex.c b/lib/isc/lex.c

index ca5fe6d..b0152eb 100644

--- a/lib/isc/lex.c

+++ b/lib/isc/lex.c

@@ -433,15 +433,11 @@ isc_lex_gettoken(isc_lex_t *lex, unsigned int options, isc_token_t *tokenp) {

 			if (source->is_file) {

 				stream = source->input;

-#if defined(HAVE_FLOCKFILE) && defined(HAVE_GETC_UNLOCKED)

-				c = getc_unlocked(stream);

-#else

-				c = getc(stream);

-#endif

-				if (c == EOF) {

-					if (ferror(stream)) {

-						source->result = ISC_R_IOERROR;

-						result = source->result;

+				result = isc_stdio_fgetc(stream, &c);

+

+				if (result != ISC_R_SUCCESS) {

+					if (result != ISC_R_EOF) {

+						source->result = result;

 						goto done;

 					}

 					source->at_eof = true;

diff --git a/lib/isc/unix/errno2result.c b/lib/isc/unix/errno2result.c

index d72d56f..4287ff3 100644

--- a/lib/isc/unix/errno2result.c

+++ b/lib/isc/unix/errno2result.c

@@ -42,6 +42,7 @@ isc___errno2result(int posixerrno, bool dolog,

 	case EINVAL:		/* XXX sometimes this is not for files */

 	case ENAMETOOLONG:

 	case EBADF:

+	case EISDIR:

 		return (ISC_R_INVALIDFILE);

 	case ENOENT:

 		return (ISC_R_FILENOTFOUND);

diff --git a/lib/isc/unix/stdio.c b/lib/isc/unix/stdio.c

index d2b1dda..79630b2 100644

--- a/lib/isc/unix/stdio.c

+++ b/lib/isc/unix/stdio.c

@@ -141,3 +141,22 @@ isc_stdio_sync(FILE *f) {

 		return (isc__errno2result(errno));

 }

+isc_result_t

+isc_stdio_fgetc(FILE *f, int *ret) {

+	int r;

+	isc_result_t result = ISC_R_SUCCESS;

+

+#if defined(HAVE_FLOCKFILE) && defined(HAVE_GETCUNLOCKED)

+	r = fgetc_unlocked(f);

+#else

+	r = fgetc(f);

+#endif

+

+	if (r == EOF)

+		result = ferror(f) ? isc__errno2result(errno) : ISC_R_EOF;

+

+	*ret = r;

+

+	return result;

+}

+