diff --git a/disk-image.c b/disk-image.c
index 9b301c6..a6d1e96 100644
--- a/disk-image.c
+++ b/disk-image.c
@@ -6,6 +6,7 @@
 #include <inttypes.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -14,6 +15,19 @@
 #define SECTOR_SHIFT		9
 #define SECTOR_SIZE		(1UL << SECTOR_SHIFT)
 
+static const char QCOW_MAGIC[]	= { 'Q', 'F', 'I', 0xfb };
+
+struct qcow_header {
+	uint8_t			magic[5];
+};
+
+static bool disk_image__is_qcow(struct disk_image *self)
+{
+	struct qcow_header *header = self->mmap;
+
+	return !memcmp(header->magic, QCOW_MAGIC, ARRAY_SIZE(QCOW_MAGIC));
+}
+
 struct disk_image *disk_image__open(const char *filename)
 {
 	struct disk_image *self;
@@ -36,6 +50,9 @@ struct disk_image *disk_image__open(const char *filename)
 	if (self->mmap == MAP_FAILED)
 		goto failed_close_fd;
 
+	if (disk_image__is_qcow(self))
+		die("QCOW disk image format is not supported.");
+
 	return self;
 
 failed_close_fd: