diff --git a/src/lib-sieve/sieve-binary-file.c b/src/lib-sieve/sieve-binary-file.c
index 644fed97a4e15186af63df2db014a0823e8bd869..e9d1a79ca2f5718d9545f7fa74b01cb963cab6f0 100644
--- a/src/lib-sieve/sieve-binary-file.c
+++ b/src/lib-sieve/sieve-binary-file.c
@@ -34,7 +34,7 @@
 #define SIEVE_BINARY_MAGIC_OTHER_ENDIAN         0xbebafeca
 
 #define SIEVE_BINARY_ALIGN(offset) \
-	(((offset) + 3) & ~3)
+	(((offset) + 3) & ~3U)
 #define SIEVE_BINARY_ALIGN_PTR(ptr) \
 	((void *) SIEVE_BINARY_ALIGN(((size_t) ptr)))