diff --git a/lib/842/842_decompress.c b/lib/842/842_decompress.c
index 87d1e0f8a492..45a9815abd63 100644
--- a/lib/842/842_decompress.c
+++ b/lib/842/842_decompress.c
@@ -309,7 +309,7 @@ int sw842_decompress(const u8 *in, unsigned int ilen,
 			if (ret)
 				return ret;
 
-			if (p.out == out) /* no previous bytes */
+			if (p.out - p.ostart < 8) /* no complete previous block */
 				return -EINVAL;
 
 			/* copy rep + 1 */