diff --git a/ChangeLog b/ChangeLog
index ef0c15f4b..0972348fd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,7 @@
 2018-02-05  Richard Frith-Macdonald <rfm@gnu.org>
 
 	* Source/NSPortCoder.m: Remove redundant (always true) conditional.
+	Use cast to mask 64bit values.
 	* Source/NSUnarchiver.m: Remove redundant (always true) conditional.
 	* Source/NSPropertyList.m: Remove dead code
 	* Source/NSDecimal.m: Remove dead code
diff --git a/Source/NSPortCoder.m b/Source/NSPortCoder.m
index 423ef4501..d5a28bfae 100644
--- a/Source/NSPortCoder.m
+++ b/Source/NSPortCoder.m
@@ -1205,21 +1205,21 @@ scalarSize(char type)
       switch (size)
         {
           case 1:
-            if (big & ~0xff)
+            if (big & (uint64_t)~0xff)
               {
                 NSLog(@"Loss of information converting decoded value to uint8_t");
               }
             *(uint8_t*)address = (uint8_t)big;
             return;
           case 2:
-            if (big & ~0xffff)
+            if (big & (uint64_t)~0xffff)
               {
                 NSLog(@"Loss of information converting decoded value to uint16_t");
               }
             *(uint16_t*)address = (uint16_t)big;
             return;
           case 4:
-            if (big & ~0xffffffff)
+            if (big & (uint64_t)~0xffffffff)
               {
                 NSLog(@"Loss of information converting decoded value to uint32_t");
               }