diff --git a/lib/bit.h b/lib/bit.h
index 076e01a0..d5b94dae 100644
--- a/lib/bit.h
+++ b/lib/bit.h
@@ -14,6 +14,11 @@
 #include <limits.h>
 
 
+#ifndef ULONG_WIDTH
+#define ULONG_WIDTH (sizeof(unsigned long) * CHAR_BIT)
+#endif
+
+
 inline unsigned long bit_ceilul(unsigned long x);
 inline unsigned long bit_ceil_wrapul(unsigned long x);
 inline int leading_zerosul(unsigned long x);