diff --git a/lib/jkqtcommon/jkqtpbasicimagetools.h b/lib/jkqtcommon/jkqtpbasicimagetools.h
index 6417e75dfe..9911d2831c 100644
--- a/lib/jkqtcommon/jkqtpbasicimagetools.h
+++ b/lib/jkqtcommon/jkqtpbasicimagetools.h
@@ -657,7 +657,7 @@ inline void JKQTPImagePlot_array2RGBimage(const T* dbl_in, int width, int height
     T* dbllog=nullptr;
     if (logScale) {
         double logB=log10(logBase);
-        dbllog=static_cast<T*>(malloc(width*height*sizeof(T)));
+        dbllog=static_cast<T*>(malloc(static_cast<size_t>(width)*static_cast<size_t>(height)*sizeof(T)));
         //memcpy(dbl, dbl_in, width*height*sizeof(T));
         for (int i=0; i<width*height; i++) {
             dbllog[i]=log10(dbl_in[i])/logB;
diff --git a/lib/jkqtplotter/graphs/jkqtpcontour.cpp b/lib/jkqtplotter/graphs/jkqtpcontour.cpp
index faf2ed456d..a356f044ea 100644
--- a/lib/jkqtplotter/graphs/jkqtpcontour.cpp
+++ b/lib/jkqtplotter/graphs/jkqtpcontour.cpp
@@ -63,7 +63,7 @@ void JKQTPContourPlot::draw(JKQTPEnhancedPainter &painter)
 
     int64_t colChecksum=-1;
     if (data && Nx*Ny>0) {
-        colChecksum=static_cast<int64_t>(qChecksum(reinterpret_cast<const char*>(data), Nx*Ny* getSampleSize()/sizeof(char)));
+        colChecksum=static_cast<int64_t>(qChecksum(reinterpret_cast<const char*>(data), static_cast<int64_t>(Nx)*static_cast<int64_t>(Ny)* static_cast<int64_t>(getSampleSize()/sizeof(char))));
     }
     /*if (parent && parent->getDatastore() && imageColumn>=0) {
         colChecksum=static_cast<int64_t>(parent->getDatastore()->getColumnChecksum(imageColumn));