--- a/tests.c
+++ b/tests.c
@@ -27,6 +27,9 @@
 #define PROGRESSOFTEN 2500
 #define ONE 0x00000001L
 
+union mword8_type mword8;
+union mword16_type mword16;
+
 /* Function definitions. */
 
 int compare_regions(ulv *bufa, ulv *bufb, size_t count) {
--- a/types.h
+++ b/types.h
@@ -25,12 +25,12 @@
     int (*fp)();
 };
 
-union {
+union mword8_type {
     unsigned char bytes[UL_LEN/8];
     ul val;
-} mword8;
+};
 
-union {
+union mword16_type {
     unsigned short u16s[UL_LEN/16];
     ul val;
-} mword16;
+};
