diff --git a/src/cli.cc b/src/cli.cc
index 992cf6d..300496d 100644
--- a/src/cli.cc
+++ b/src/cli.cc
@@ -190,6 +190,8 @@ static ot::status process(ot::ogg_reader& reader, ot::ogg_writer* writer, const
 		ot::status rc = reader.next_page();
 		if (rc == ot::st::end_of_stream)
 			break;
+		else if (rc == ot::st::bad_stream && absolute_page_no == 0)
+			return {ot::st::bad_stream, "Input is not a valid Ogg file."};
 		else if (rc != ot::st::ok)
 			return rc;
 		auto serialno = ogg_page_serialno(&reader.page);
diff --git a/src/ogg.cc b/src/ogg.cc
index 2ee21c5..281ee8e 100644
--- a/src/ogg.cc
+++ b/src/ogg.cc
@@ -25,19 +25,25 @@ bool ot::is_opus_stream(const ogg_page& identification_header)
 
 ot::status ot::ogg_reader::next_page()
 {
-	while (ogg_sync_pageout(&sync, &page) != 1) {
-		if (feof(file))
-			return {st::end_of_stream, "End of stream was reached"};
+	int rc;
+	while ((rc = ogg_sync_pageout(&sync, &page)) != 1) {
+		if (rc == -1)
+			return {st::bad_stream, "Unsynced data in stream."};
+		if (ogg_sync_check(&sync) != 0)
+			return {st::libogg_error, "ogg_sync_check signalled an error."};
+		if (feof(file)) {
+			if (sync.fill != sync.returned)
+				return {st::bad_stream, "Unsynced data at end of stream."};
+			return {st::end_of_stream, "End of stream was reached."};
+		}
 		char* buf = ogg_sync_buffer(&sync, 65536);
 		if (buf == nullptr)
-			return {st::libogg_error, "ogg_sync_buffer failed"};
+			return {st::libogg_error, "ogg_sync_buffer failed."};
 		size_t len = fread(buf, 1, 65536, file);
 		if (ferror(file))
 			return {st::standard_error, "fread error: "s + strerror(errno)};
 		if (ogg_sync_wrote(&sync, len) != 0)
-			return {st::libogg_error, "ogg_sync_wrote failed"};
-		if (ogg_sync_check(&sync) != 0)
-			return {st::libogg_error, "ogg_sync_check failed"};
+			return {st::libogg_error, "ogg_sync_wrote failed."};
 	}
 	return st::ok;
 }
diff --git a/src/opustags.h b/src/opustags.h
index d851eb9..37b82c7 100644
--- a/src/opustags.h
+++ b/src/opustags.h
@@ -56,6 +56,7 @@ enum class st {
 	standard_error, /**< Error raised by the C standard library. */
 	int_overflow,
 	/* Ogg */
+	bad_stream,
 	end_of_stream,
 	libogg_error,
 	/* Opus */
diff --git a/t/ogg.cc b/t/ogg.cc
index f4b6181..1c170d8 100644
--- a/t/ogg.cc
+++ b/t/ogg.cc
@@ -116,6 +116,16 @@ static void check_memory_ogg()
 	}
 }
 
+void check_bad_stream()
+{
+	auto err_msg = "did not detect the stream is not an ogg stream";
+	ot::file input = fmemopen((void*) err_msg, 20, "r");
+	ot::ogg_reader reader(input.get());
+	ot::status rc = reader.next_page();
+	if (rc != ot::st::bad_stream)
+		throw failure(err_msg);
+}
+
 void check_identification()
 {
 	auto good_header = (unsigned char*)
@@ -151,9 +161,10 @@ void check_identification()
 
 int main(int argc, char **argv)
 {
-	std::cout << "1..3\n";
+	std::cout << "1..4\n";
 	run(check_ref_ogg, "check a reference ogg stream");
 	run(check_memory_ogg, "build and check a fresh stream");
+	run(check_bad_stream, "read a non-ogg stream");
 	run(check_identification, "stream identification");
 	return 0;
 }
diff --git a/t/opustags.t b/t/opustags.t
index 06962d8..bf9f6a2 100644
--- a/t/opustags.t
+++ b/t/opustags.t
@@ -4,7 +4,7 @@ use strict;
 use warnings;
 use utf8;
 
-use Test::More tests => 27;
+use Test::More tests => 28;
 
 use Digest::MD5;
 use File::Basename;
@@ -73,6 +73,10 @@ is_deeply(opustags('--derp'), ['', <<"EOF", 256], 'unrecognized option shows an
 error: Unrecognized option '--derp'.
 EOF
 
+is_deeply(opustags('../opustags'), ['', <<"EOF", 256], 'not an Ogg stream');
+error: Input is not a valid Ogg file.
+EOF
+
 ####################################################################################################
 # Test the main features of opustags on an Ogg Opus sample file.