diff --git a/pngrutil.c b/pngrutil.c
index 320ebb9..9458868 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1114,7 +1114,7 @@
    /* There should be at least one zero (the compression type byte)
     * following the separator, and we should be on it
     */
-   if (slength < 1 ||  profile >= png_ptr->chunkdata + slength - 1)
+   if (slength < 1U ||  profile >= png_ptr->chunkdata + slength - 1U)
    {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
@@ -1242,7 +1242,8 @@
    ++entry_start;
 
    /* A sample depth should follow the separator, and we should be on it  */
-   if (slength < 2 || entry_start > (png_bytep)png_ptr->chunkdata + slength - 2)
+   if (slength < 2U ||
+       entry_start > (png_bytep)png_ptr->chunkdata + slength - 2U)
    {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
@@ -1716,7 +1717,7 @@
 
    /* We need to have at least 12 bytes after the purpose string
       in order to get the parameter information. */
-   if (slength < 12 || endptr <= buf + 12)
+   if (slength < 12U || endptr - buf <= 12)
    {
       png_warning(png_ptr, "Invalid pCAL data");
       png_free(png_ptr, png_ptr->chunkdata);
@@ -2172,7 +2173,7 @@
       /* Empty loop */ ;
 
    /* zTXt must have some text after the chunkdataword */
-   if (slength < 2 || text >= png_ptr->chunkdata + slength - 2)
+   if (slength < 2U || text >= png_ptr->chunkdata + slength - 2U)
    {
       png_warning(png_ptr, "Truncated zTXt chunk");
       png_free(png_ptr, png_ptr->chunkdata);
@@ -2298,7 +2299,7 @@
     * keyword
     */
 
-   if (slength < 3 || lang >= png_ptr->chunkdata + slength - 3)
+   if (slength < 3U || lang >= png_ptr->chunkdata + slength - 3U)
    {
       png_warning(png_ptr, "Truncated iTXt chunk");
       png_free(png_ptr, png_ptr->chunkdata);