diff --git a/src/amd/common/sid.h b/src/amd/common/sid.h
index e922b38ae3a..30cfeb9368f 100644
--- a/src/amd/common/sid.h
+++ b/src/amd/common/sid.h
@@ -9123,7 +9123,9 @@
 #define    CIK_SDMA_PACKET_SEMAPHORE               0x7
 #define    CIK_SDMA_PACKET_CONSTANT_FILL           0xb
 #define    CIK_SDMA_PACKET_SRBM_WRITE              0xe
-#define    CIK_SDMA_COPY_MAX_SIZE                  0x3fffe0
+/* There is apparently an undocumented HW "feature" that
+   prevents the HW from copying past 256 bytes of (1 << 22) */
+#define    CIK_SDMA_COPY_MAX_SIZE                  0x3fff00
 
 enum amd_cmp_class_flags {
 	S_NAN = 1 << 0,        // Signaling NaN