diff --git a/include/asm-generic/bitops/fls64.h b/include/asm-generic/bitops/fls64.h
index 1b6b17ce2428091e605c8cbda7103b1d42836780..86d403f8b256815761270e822b84b438cc87f5d2 100644
--- a/include/asm-generic/bitops/fls64.h
+++ b/include/asm-generic/bitops/fls64.h
@@ -3,6 +3,18 @@
 
 #include <asm/types.h>
 
+/**
+ * fls64 - find last set bit in a 64-bit word
+ * @x: the word to search
+ *
+ * This is defined in a similar way as the libc and compiler builtin
+ * ffsll, but returns the position of the most significant set bit.
+ *
+ * fls64(value) returns 0 if value is 0 or the position of the last
+ * set bit if value is nonzero. The last (most significant) bit is
+ * at position 64.
+ */
+#if BITS_PER_LONG == 32
 static inline int fls64(__u64 x)
 {
 	__u32 h = x >> 32;
@@ -10,5 +22,15 @@ static inline int fls64(__u64 x)
 		return fls(h) + 32;
 	return fls(x);
 }
+#elif BITS_PER_LONG == 64
+static inline int fls64(__u64 x)
+{
+	if (x == 0)
+		return 0;
+	return __fls(x) + 1;
+}
+#else
+#error BITS_PER_LONG not 32 or 64
+#endif
 
 #endif /* _ASM_GENERIC_BITOPS_FLS64_H_ */
diff --git a/include/asm-x86/bitops_64.h b/include/asm-x86/bitops_64.h
index a5fbe7a02a3f60bf79f91a08ea9ba2a9f05eec09..d13352087191b7b8a7a6cbd2e02e9ab671917da4 100644
--- a/include/asm-x86/bitops_64.h
+++ b/include/asm-x86/bitops_64.h
@@ -39,25 +39,14 @@ static inline void set_bit_string(unsigned long *bitmap, unsigned long i,
 
 #include <asm-generic/bitops/sched.h>
 
-/**
- * fls64 - find last bit set in 64 bit word
- * @x: the word to search
- *
- * This is defined the same way as fls.
- */
-static inline int fls64(__u64 x)
-{
-	if (x == 0)
-		return 0;
-	return __fls(x) + 1;
-}
-
 #define ARCH_HAS_FAST_MULTIPLIER 1
 
 #include <asm-generic/bitops/hweight.h>
 
 #endif /* __KERNEL__ */
 
+#include <asm-generic/bitops/fls64.h>
+
 #ifdef __KERNEL__
 
 #include <asm-generic/bitops/ext2-non-atomic.h>