diff --git a/src/workers/Hashrate.cpp b/src/workers/Hashrate.cpp
index 247c36ee..160306c6 100644
--- a/src/workers/Hashrate.cpp
+++ b/src/workers/Hashrate.cpp
@@ -21,6 +21,12 @@
  *   along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifdef _WIN32
+#define isnormal(x) (_fpclass(x) == _FPCLASS_NN || _fpclass(x) == _FPCLASS_PN)
+#else
+#include <math.h>
+#endif
+
 #ifndef _WIN32
 #if __cplusplus <= 199711L
 #include <sys/time.h>
@@ -65,10 +71,15 @@ static int gettimeofday(struct timeval* tp, struct timezone* tzp)
 #include "workers/Hashrate.h"
 
 
-inline const char* format(double h, char* buf, size_t size)
+inline std::string format(const double value)
 {
-	snprintf(buf, size, "%03.1f", h);
-	return buf;
+	char buff[8];
+	if(false == isnormal(value) && 0 != value)
+	{
+		return "n/a";
+	}
+	snprintf(buff, sizeof(buff), "%03.1f", value);
+	return buff;
 }
 
 
@@ -190,14 +201,11 @@ void Hashrate::add(size_t threadId, uint64_t count, uint64_t timestamp)
 
 void Hashrate::print()
 {
-	char num1[8];
-	char num2[8];
-	char num3[8];
-	char num4[8];
-
-	LOG_INFO("speed 2.5s/60s/15m " << format(calc(ShortInterval),  num1,
-	         sizeof(num1)) << " " << format(calc(MediumInterval), num2, sizeof(num2)) << " " << format(calc(LargeInterval),
-	                 num3, sizeof(num3)) << " H/s max: " << format(m_highest, num4, sizeof(num4)) << " H/s");
+	LOG_INFO("speed 2.5s/60s/15m " <<
+	         format(calc(ShortInterval)) << " " <<
+	         format(calc(MediumInterval)) << " " <<
+	         format(calc(LargeInterval)) << " H/s max: " <<
+	         format(m_highest) << " H/s");
 }
 
 
@@ -210,7 +218,7 @@ void Hashrate::stop()
 void Hashrate::updateHighest()
 {
 	double highest = calc(ShortInterval);
-	if(0 != highest && highest > m_highest)
+	if(isnormal(highest) && highest > m_highest)
 	{
 		m_highest = highest;
 	}