diff --git a/src/adb.c b/src/adb.c
index 69b58fb..1fc135c 100644
--- a/src/adb.c
+++ b/src/adb.c
@@ -257,7 +257,10 @@ err:
 int adb_m_process(struct adb *db, struct apk_istream *is, uint32_t expected_schema,
 	struct apk_trust *t, int (*cb)(struct adb *, struct adb_block *, struct apk_istream *))
 {
-	apk_blob_t mmap = apk_istream_mmap(is);
+	apk_blob_t mmap;
+
+	if (IS_ERR(is)) return PTR_ERR(is);
+	mmap = apk_istream_mmap(is);
 	memset(db, 0, sizeof *db);
 	if (expected_schema & ADB_SCHEMA_IMPLIED)
 		db->schema = expected_schema & ~ADB_SCHEMA_IMPLIED;
diff --git a/src/adb_comp.c b/src/adb_comp.c
index b697101..26fb50f 100644
--- a/src/adb_comp.c
+++ b/src/adb_comp.c
@@ -11,13 +11,14 @@
 
 struct apk_istream *adb_decompress(struct apk_istream *is, adb_comp_t *compression)
 {
-	 adb_comp_t c = -1;
+	adb_comp_t c = -1;
 
 	if (IS_ERR_OR_NULL(is)) return is;
 
 	uint8_t *buf = apk_istream_peek(is, 4);
 	if (IS_ERR(buf)) return ERR_PTR(apk_istream_close_error(is, PTR_ERR(buf)));
-	if (memcmp(buf, "ADB", 3) == 0) switch (buf[3]) {
+	if (memcmp(buf, "ADB", 3) != 0) return ERR_PTR(apk_istream_close_error(is, -APKE_ADB_HEADER));
+	switch (buf[3]) {
 	case '.':
 		c = ADB_COMP_NONE;
 		break;