diff --git a/CHANGES b/CHANGES
index 60d0c4cbfc..959a8d32ec 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+5030.	[bug]		Align CMSG buffers to a 64-bit boundary, fixes crash
+			on architectures with strict alignment. [GL #521]
+
 	--- 9.13.3 released ---
 
 5029.	[func]		Workarounds for servers that misbehave when queried
diff --git a/lib/isc/include/isc/util.h b/lib/isc/include/isc/util.h
index bb0c8854a8..acc3d64c64 100644
--- a/lib/isc/include/isc/util.h
+++ b/lib/isc/include/isc/util.h
@@ -259,6 +259,11 @@ extern void mock_assert(const int result, const char* const expression,
  */
 #define TIME_NOW(tp) 	RUNTIME_CHECK(isc_time_now((tp)) == ISC_R_SUCCESS)
 
+/*%
+ * Alignment
+ */
+#define ALIGN(x, a) (((x) + (a) - 1) & ~((typeof(x))(a)-1))
+
 /*%
  * Misc
  */
diff --git a/lib/isc/unix/socket.c b/lib/isc/unix/socket.c
index 343cec2234..62a00cddac 100644
--- a/lib/isc/unix/socket.c
+++ b/lib/isc/unix/socket.c
@@ -315,8 +315,9 @@ typedef isc_event_t intev_t;
 
 #define CMSG_SP_INT 24
 
-#define RECVCMSGBUFLEN (2*(CMSG_SP_IN6PKT + CMSG_SP_TIMESTAMP + CMSG_SP_TCTOS)+1)
-#define SENDCMSGBUFLEN (2*(CMSG_SP_IN6PKT + CMSG_SP_INT + CMSG_SP_TCTOS)+1)
+/* Align cmsg buffers to be safe on SPARC etc. */
+#define RECVCMSGBUFLEN ALIGN(2*(CMSG_SP_IN6PKT + CMSG_SP_TIMESTAMP + CMSG_SP_TCTOS)+1, sizeof(void*))
+#define SENDCMSGBUFLEN ALIGN(2*(CMSG_SP_IN6PKT + CMSG_SP_INT + CMSG_SP_TCTOS)+1, sizeof(void*))
 
 /*%
  * The number of times a send operation is repeated if the result is EINTR.