--- butteraugli/butteraugli.cc
+++ butteraugli/butteraugli.cc
@@ -107,7 +107,7 @@ static inline void CheckImage(const ImageF &image, const char *name) {
     const float * const BUTTERAUGLI_RESTRICT row = image.Row(y);
     for (size_t x = 0; x < image.xsize(); ++x) {
       if (IsNan(row[x])) {
-        printf("Image %s @ %lu,%lu (of %lu,%lu)\n", name, x, y, image.xsize(),
+        printf("Image %s @ %zu,%zu (of %zu,%zu)\n", name, x, y, image.xsize(),
                image.ysize());
         exit(1);
       }
--- butteraugli/butteraugli.h
+++ butteraugli/butteraugli.h
@@ -216,7 +216,7 @@ class Image {
  public:
   using T = ComponentType;
 
-  Image() : xsize_(0), ysize_(0), bytes_per_row_(0), bytes_(nullptr, Ignore) {}
+  Image() : xsize_(0), ysize_(0), bytes_per_row_(0), bytes_(static_cast<uint8_t*>(nullptr), Ignore) {}
 
   Image(const size_t xsize, const size_t ysize)
       : xsize_(xsize),
--- butteraugli/butteraugli_main.cc
+++ butteraugli/butteraugli_main.cc
@@ -2,6 +2,7 @@
 #include <cstdint>
 #include <cstdio>
 #include <vector>
+#include <algorithm>
 #include "butteraugli/butteraugli.h"
 
 extern "C" {
@@ -378,7 +379,7 @@ int Run(int argc, char* argv[]) {
     // Adding a missing alpha channel to one of the images.
     rgb2.push_back(Image8(rgb2[0].xsize(), rgb2[0].ysize(), 255));
   } else if (rgb1.size() != rgb2.size()) {
-    fprintf(stderr, "Different number of channels: %lu vs %lu\n", rgb1.size(),
+    fprintf(stderr, "Different number of channels: %zu vs %zu\n", rgb1.size(),
             rgb2.size());
     exit(1);
   }
@@ -387,7 +388,7 @@ int Run(int argc, char* argv[]) {
     if (rgb1[c].xsize() != rgb2[c].xsize() ||
         rgb1[c].ysize() != rgb2[c].ysize()) {
       fprintf(
-          stderr, "The images are not equal in size: (%lu,%lu) vs (%lu,%lu)\n",
+          stderr, "The images are not equal in size: (%zu,%zu) vs (%zu,%zu)\n",
           rgb1[c].xsize(), rgb2[c].xsize(), rgb1[c].ysize(), rgb2[c].ysize());
       return 1;
     }
@@ -439,7 +440,7 @@ int Run(int argc, char* argv[]) {
       return 1;
     }
     bool ok = true;
-    if (fprintf(fmap, "P6\n%lu %lu\n255\n",
+    if (fprintf(fmap, "P6\n%zu %zu\n255\n",
                       rgb1[0].xsize(), rgb1[0].ysize()) < 0){
       perror("fprintf");
       ok = false;