diff --git a/src/piotr_fhog/gradientMex.cpp b/src/piotr_fhog/gradientMex.cpp
index 98d2882d..54f335cc 100644
--- a/src/piotr_fhog/gradientMex.cpp
+++ b/src/piotr_fhog/gradientMex.cpp
@@ -301,7 +301,7 @@ void fhog( float *M, float *O, float *H, int h, int w, int binSize,
   const int hb=h/binSize, wb=w/binSize, nb=hb*wb, nbo=nb*nOrients;
   float *N, *R1, *R2; int o, x;
   // compute unnormalized constrast sensitive histograms
-  R1 = (float*) wrCalloc(wb*hb*nOrients*2,sizeof(float));
+  R1 = (float*) wrCalloc(wb*hb*nOrients*2 + 2,sizeof(float));
   gradHist( M, O, R1, h, w, binSize, nOrients*2, softBin, true );
   // compute unnormalized contrast insensitive histograms
   R2 = (float*) wrCalloc(wb*hb*nOrients,sizeof(float));