diff --git a/stb_image.h b/stb_image.h
index 482d23c..708dc95 100644
--- a/stb_image.h
+++ b/stb_image.h
@@ -6386,6 +6386,7 @@ static stbi_uc *stbi__process_gif_raster(stbi__context *s, stbi__gif *g)
 // two back is the image from two frames ago, used for a very specific disposal format
 static stbi_uc *stbi__gif_load_next(stbi__context *s, stbi__gif *g, int *comp, int req_comp, stbi_uc *two_back)
 {
+   STBI_NOTUSED(req_comp);
    int dispose; 
    int first_frame; 
    int pi; 
@@ -6610,6 +6611,7 @@ static void *stbi__load_gif_main(stbi__context *s, int **delays, int *x, int *y,
 
 static void *stbi__gif_load(stbi__context *s, int *x, int *y, int *comp, int req_comp, stbi__result_info *ri)
 {
+   STBI_NOTUSED(ri);
    stbi_uc *u = 0;
    stbi__gif g;
    memset(&g, 0, sizeof(g));
diff --git a/stb_image_write.h b/stb_image_write.h
index c6bd5e2..89bfb2b 100644
--- a/stb_image_write.h
+++ b/stb_image_write.h
@@ -1068,7 +1068,7 @@ static void stbiw__encode_png_line(unsigned char *pixels, int stride_bytes, int
    }
 }
 
-unsigned char *stbi_write_png_to_mem(unsigned char *pixels, int stride_bytes, int x, int y, int n, int *out_len)
+unsigned char *stbi_write_png_to_mem(const unsigned char *pixels, int stride_bytes, int x, int y, int n, int *out_len)
 {
    int force_filter = stbi_write_force_png_filter;
    int ctype[5] = { -1, 0, 4, 2, 6 };
@@ -1090,11 +1090,11 @@ unsigned char *stbi_write_png_to_mem(unsigned char *pixels, int stride_bytes, in
       int filter_type;
       if (force_filter > -1) {
          filter_type = force_filter;
-         stbiw__encode_png_line(pixels, stride_bytes, x, y, j, n, force_filter, line_buffer);
+         stbiw__encode_png_line(const_cast<unsigned char*>(pixels), stride_bytes, x, y, j, n, force_filter, line_buffer);
       } else { // Estimate the best filter by running through all of them:
          int best_filter = 0, best_filter_val = 0x7fffffff, est, i;
          for (filter_type = 0; filter_type < 5; filter_type++) {
-            stbiw__encode_png_line(pixels, stride_bytes, x, y, j, n, filter_type, line_buffer);
+            stbiw__encode_png_line(const_cast<unsigned char*>(pixels), stride_bytes, x, y, j, n, filter_type, line_buffer);
 
             // Estimate the entropy of the line using this filter; the less, the better.
             est = 0;
@@ -1107,7 +1107,7 @@ unsigned char *stbi_write_png_to_mem(unsigned char *pixels, int stride_bytes, in
             }
          }
          if (filter_type != best_filter) {  // If the last iteration already got us the best filter, don't redo it
-            stbiw__encode_png_line(pixels, stride_bytes, x, y, j, n, best_filter, line_buffer);
+            stbiw__encode_png_line(const_cast<unsigned char*>(pixels), stride_bytes, x, y, j, n, best_filter, line_buffer);
             filter_type = best_filter;
          }
       }
@@ -1159,7 +1159,7 @@ STBIWDEF int stbi_write_png(char const *filename, int x, int y, int comp, const
 {
    FILE *f;
    int len;
-   unsigned char *png = stbi_write_png_to_mem((unsigned char *) data, stride_bytes, x, y, comp, &len);
+   unsigned char *png = stbi_write_png_to_mem((const unsigned char *) data, stride_bytes, x, y, comp, &len);
    if (png == NULL) return 0;
 
    f = stbiw__fopen(filename, "wb");
@@ -1174,7 +1174,7 @@ STBIWDEF int stbi_write_png(char const *filename, int x, int y, int comp, const
 STBIWDEF int stbi_write_png_to_func(stbi_write_func *func, void *context, int x, int y, int comp, const void *data, int stride_bytes)
 {
    int len;
-   unsigned char *png = stbi_write_png_to_mem((unsigned char *) data, stride_bytes, x, y, comp, &len);
+   unsigned char *png = stbi_write_png_to_mem((const unsigned char *) data, stride_bytes, x, y, comp, &len);
    if (png == NULL) return 0;
    func(context, png, len);
    STBIW_FREE(png);