diff --git a/src/opus.cc b/src/opus.cc
index 9d0315d..067cc21 100644
--- a/src/opus.cc
+++ b/src/opus.cc
@@ -34,34 +34,41 @@
 #define le32toh(x) OSSwapLittleToHostInt32(x)
 #endif
 
-int ot::parse_tags(const char *data, long len, opus_tags *tags)
+ot::parse_result ot::parse_tags(const char *data, long len, opus_tags *tags)
 {
 	long pos;
-	if (len < 8+4+4)
-		return -1;
-	if (strncmp(data, "OpusTags", 8) != 0)
-		return -1;
+	if (8 > len)
+		return parse_result::overflowing_magic_number;
+	if (memcmp(data, "OpusTags", 8) != 0)
+		return parse_result::bad_magic_number;
 	// Vendor
 	pos = 8;
-	tags->vendor = ot::string_view(data + pos + 4, le32toh(*((uint32_t*) (data + pos))));
-	pos += 4 + tags->vendor.size();
 	if (pos + 4 > len)
-		return -1;
+		return parse_result::overflowing_vendor_length;
+	size_t vendor_length = le32toh(*((uint32_t*) (data + pos)));
+	if (pos + 4 + vendor_length > len)
+		return parse_result::overflowing_vendor_data;
+	tags->vendor = ot::string_view(data + pos + 4, vendor_length);
+	pos += 4 + tags->vendor.size();
 	// Count
+	if (pos + 4 > len)
+		return parse_result::overflowing_comment_count;
 	uint32_t count = le32toh(*((uint32_t*) (data + pos)));
 	pos += 4;
 	// Comments
 	for (uint32_t i = 0; i < count; ++i) {
+		if (pos + 4 > len)
+			return parse_result::overflowing_comment_length;
 		uint32_t comment_length = le32toh(*((uint32_t*) (data + pos)));
+		if (pos + 4 + comment_length > len)
+			return parse_result::overflowing_comment_data;
 		const char *comment_value = data + pos + 4;
 		tags->comments.emplace_back(comment_value, comment_length);
 		pos += 4 + comment_length;
-		if (pos > len)
-			return -1;
 	}
 	// Extra data
 	tags->extra_data = ot::string_view(data + pos, static_cast<size_t>(len - pos));
-	return 0;
+	return parse_result::ok;
 }
 
 int ot::render_tags(opus_tags *tags, ogg_packet *op)
diff --git a/src/opustags.cc b/src/opustags.cc
index 3ca5bb4..3865e9f 100644
--- a/src/opustags.cc
+++ b/src/opustags.cc
@@ -256,7 +256,7 @@ int main(int argc, char **argv){
                 }
             }
             else if(packet_count == 2){ // Comment header
-                if(ot::parse_tags((char*) op.packet, op.bytes, &tags) == -1){
+                if(ot::parse_tags((char*) op.packet, op.bytes, &tags) != ot::parse_result::ok){
                     error = "opustags: invalid comment header";
                     break;
                 }
diff --git a/src/opustags.h b/src/opustags.h
index ced1791..847cad3 100644
--- a/src/opustags.h
+++ b/src/opustags.h
@@ -83,7 +83,18 @@ struct opus_tags {
 	string_view extra_data;
 };
 
-int parse_tags(const char *data, long len, opus_tags *tags);
+enum class parse_result {
+	ok = 0,
+	bad_magic_number = -100,
+	overflowing_magic_number,
+	overflowing_vendor_length,
+	overflowing_vendor_data,
+	overflowing_comment_count,
+	overflowing_comment_length,
+	overflowing_comment_data,
+};
+
+parse_result parse_tags(const char *data, long len, opus_tags *tags);
 int render_tags(opus_tags *tags, ogg_packet *op);
 void delete_tags(opus_tags *tags, const char *field);
 
diff --git a/t/unit.cc b/t/unit.cc
index adc8161..6f18d89 100644
--- a/t/unit.cc
+++ b/t/unit.cc
@@ -39,9 +39,9 @@ static const char standard_OpusTags[] =
 static bool parse_standard()
 {
 	ot::opus_tags tags;
-	int rc = ot::parse_tags(standard_OpusTags, sizeof(standard_OpusTags) - 1, &tags);
-	if (rc != 0)
-		throw failure("ot::parse_tags did not return 0");
+	auto rc = ot::parse_tags(standard_OpusTags, sizeof(standard_OpusTags) - 1, &tags);
+	if (rc != ot::parse_result::ok)
+		throw failure("ot::parse_tags did not return ok");
 	if (tags.vendor != ot::string_view( "opustags test packet"))
 		throw failure("bad vendor string");
 	if (tags.comments.size() != 2)
@@ -60,12 +60,11 @@ static bool parse_standard()
 static bool recode_standard()
 {
 	ot::opus_tags tags;
-	int rc = ot::parse_tags(standard_OpusTags, sizeof(standard_OpusTags) - 1, &tags);
-	if (rc != 0)
-		throw failure("ot::parse_tags did not return 0");
+	auto rc = ot::parse_tags(standard_OpusTags, sizeof(standard_OpusTags) - 1, &tags);
+	if (rc != ot::parse_result::ok)
+		throw failure("ot::parse_tags did not return ok");
 	ogg_packet packet;
-	rc = ot::render_tags(&tags, &packet);
-	if (rc != 0)
+	if (ot::render_tags(&tags, &packet) != 0)
 		throw failure("ot::render_tags did not return 0");
 	if (packet.b_o_s != 0)
 		throw failure("b_o_s should not be set");
@@ -89,14 +88,15 @@ static bool recode_padding()
 	std::string padded_OpusTags(standard_OpusTags, sizeof(standard_OpusTags));
 	// ^ note: padded_OpusTags ends with a null byte here
 	padded_OpusTags += "hello";
-	int rc = ot::parse_tags(padded_OpusTags.data(), padded_OpusTags.size(), &tags);
-	if (rc != 0)
-		throw failure("ot::parse_tags did not return 0");
+	auto rc = ot::parse_tags(padded_OpusTags.data(), padded_OpusTags.size(), &tags);
+	if (rc != ot::parse_result::ok)
+		throw failure("ot::parse_tags did not return ok");
 	if (tags.extra_data != ot::string_view("\0hello", 6))
 		throw failure("corrupted extra data");
 	// recode the packet and ensure it's exactly the same
 	ogg_packet packet;
-	rc = ot::render_tags(&tags, &packet);
+	if (ot::render_tags(&tags, &packet) != 0)
+		throw failure("ot::render_tags did not return 0");
 	if (packet.bytes < padded_OpusTags.size())
 		throw failure("the packet was truncated");
 	if (packet.bytes > padded_OpusTags.size())