diff --git a/app/operations/gimpcageconfig.c b/app/operations/gimpcageconfig.c
index 774489c9e6..29677f89c0 100644
--- a/app/operations/gimpcageconfig.c
+++ b/app/operations/gimpcageconfig.c
@@ -425,7 +425,6 @@ gimp_cage_config_get_bounding_box (GimpCageConfig *gcc)
   GimpCagePoint *point;
 
   g_return_val_if_fail (GIMP_IS_CAGE_CONFIG (gcc), bounding_box);
-  g_return_val_if_fail (gcc->cage_points->len >= 0, bounding_box);
 
   if (gcc->cage_points->len == 0)
     return bounding_box;
diff --git a/libgimpbase/gimpwire.c b/libgimpbase/gimpwire.c
index 87945095af..71fbb77d5d 100644
--- a/libgimpbase/gimpwire.c
+++ b/libgimpbase/gimpwire.c
@@ -96,8 +96,6 @@ gimp_wire_read (GIOChannel *channel,
                 gsize       count,
                 gpointer    user_data)
 {
-  g_return_val_if_fail (count >= 0, FALSE);
-
   if (wire_read_func)
     {
       if (!(* wire_read_func) (channel, buf, count, user_data))
@@ -167,8 +165,6 @@ gimp_wire_write (GIOChannel   *channel,
                  gsize         count,
                  gpointer      user_data)
 {
-  g_return_val_if_fail (count >= 0, FALSE);
-
   if (wire_write_func)
     {
       if (!(* wire_write_func) (channel, (guint8 *) buf, count, user_data))
diff --git a/plug-ins/common/file-xmc.c b/plug-ins/common/file-xmc.c
index c5f25139cc..caf5812e21 100644
--- a/plug-ins/common/file-xmc.c
+++ b/plug-ins/common/file-xmc.c
@@ -871,7 +871,7 @@ load_thumbnail (const gchar *filename,
           size = READ32 (fp, error)
           positions[*thumb_num_layers] = READ32 (fp, error)
           /* is this image is more preferred than selected before? */
-          diff = ABS(thumb_size - size);
+          diff = MAX (thumb_size, size) - MIN (thumb_size, size);
           if (diff < min_diff)
             {/* the image size is closer than current selected image */
               min_diff = diff;
diff --git a/plug-ins/script-fu/tinyscheme/scheme.c b/plug-ins/script-fu/tinyscheme/scheme.c
index 989fdd2f23..fc47880aa5 100644
--- a/plug-ins/script-fu/tinyscheme/scheme.c
+++ b/plug-ins/script-fu/tinyscheme/scheme.c
@@ -1651,7 +1651,8 @@ static gunichar basic_inchar(port *pt) {
       len = pt->rep.string.past_the_end - pt->rep.string.curr;
       c = g_utf8_get_char_validated(pt->rep.string.curr, len);
 
-      if (c >= 0)   /* Valid UTF-8 character? */
+      if (c != (gunichar) -1 &&
+          c != (gunichar) -2)   /* Valid UTF-8 character? */
       {
         len = g_unichar_to_utf8(c, NULL);   /* Length of UTF-8 sequence */
         pt->rep.string.curr += len;