diff --git a/Readme.txt b/Readme.txt
index 0c6f5c72..1a371398 100644
--- a/Readme.txt
+++ b/Readme.txt
@@ -54,6 +54,15 @@ The exception is computer with big-endian CPUs, like PowerPC
 Macintoshes. Some of the bitboard routines in the current version of
 Stockfish are endianness-sensitive, and won't work on a big-endian CPU.
 
+Stockfish has POPCNT instruction runtime detection and support. This can
+give an extra speed on Core i7 or similar systems. To enable this feature
+(disabled by default) simply uncomment #define USE_POPCNT in bitcount.h
+before to compile.
+
+On 64 bit Unix-like systems the 'bsfq' assembly instruction will be used
+for bit counting. Detection is automatic at compile time, but in case you
+experience compile problems you can comment out #define USE_BSFQ line in types.h
+
 
 5. Terms of use
 ---------------
diff --git a/src/bitcount.h b/src/bitcount.h
index 9a3b4811..ef841f3a 100644
--- a/src/bitcount.h
+++ b/src/bitcount.h
@@ -22,18 +22,19 @@
 #if !defined(BITCOUNT_H_INCLUDED)
 #define BITCOUNT_H_INCLUDED
 
-// To disable POPCNT support uncomment NO_POPCNT define. You should do it only
-// in PGO compiling to exercise the default fallback path. Don't forget to
-// re-comment the line for the final optimized compile though ;-)
+// To enable POPCNT support uncomment USE_POPCNT define. For PGO compile on a Core i7
+// you may want to collect profile data first with USE_POPCNT disabled and then, in a
+// second profiling session, with USE_POPCNT enabled so to exercise both paths. Don't
+// forget to leave USE_POPCNT enabled for the final optimized compile though ;-)
 
-//#define NO_POPCNT
+//#define USE_POPCNT
 
 
 #include "types.h"
 
 // Select type of intrinsic bit count instruction to use
 
-#if defined(_MSC_VER) && defined(IS_64BIT) && !defined(NO_POPCNT) // Microsoft compiler
+#if defined(_MSC_VER) && defined(IS_64BIT) && defined(USE_POPCNT) // Microsoft compiler
 
 #include <intrin.h>
 
@@ -54,7 +55,7 @@ template<typename T> unsigned __popcnt64(T) { return 0; } // Is never called
 
 #define POPCNT_INTRINSIC(x) __popcnt64(x)
 
-#elif defined(__INTEL_COMPILER) && defined(IS_64BIT) && !defined(NO_POPCNT) // Intel compiler
+#elif defined(__INTEL_COMPILER) && defined(IS_64BIT) && defined(USE_POPCNT) // Intel compiler
 
 #include <nmmintrin.h>
 
@@ -70,7 +71,7 @@ template<typename T> unsigned _mm_popcnt_u64(T) { return 0; } // Is never called
 
 #define POPCNT_INTRINSIC(x) _mm_popcnt_u64(x)
 
-#else // Safe fallback for unsupported compilers or when NO_POPCNT is defined
+#else // Safe fallback for unsupported compilers or when USE_POPCNT is disabled
 
 inline bool cpu_has_popcnt() { return false; }
 
@@ -145,12 +146,8 @@ inline int count_1s_max_15(Bitboard b) {
 
 // Global constant initialized at startup that is set to true if
 // CPU on which application runs supports POPCNT intrinsic. Unless
-// NO_POPCNT is defined.
-#if defined(NO_POPCNT)
-const bool CpuHasPOPCNT = false;
-#else
+// USE_POPCNT is not defined.
 const bool CpuHasPOPCNT = cpu_has_popcnt();
-#endif
 
 
 // Global constant used to print info about the use of 64 optimized
diff --git a/src/types.h b/src/types.h
index af5e2455..70e47079 100644
--- a/src/types.h
+++ b/src/types.h
@@ -62,7 +62,7 @@ typedef uint64_t Bitboard;
 #define IS_64BIT
 #endif
 
-#if defined(IS_64BIT) && (defined(__GNUC__) || defined(__INTEL_COMPILER))
+#if defined(IS_64BIT) && !defined(_WIN64) && (defined(__GNUC__) || defined(__INTEL_COMPILER))
 #define USE_BSFQ
 #endif