1 files changed, 8 insertions, 2 deletions
diff --git a/libdimension/png-stubs.c b/libdimension/png-stubs.c
index eca7697..db4a19d 100644
--- a/libdimension/png-stubs.c
+++ b/libdimension/png-stubs.c
@@ -19,35 +19,41 @@
  *************************************************************************/
 
 #include "dimension.h"
+#include <errno.h>
 
 /* Stubs for PNG functions when compiled with --disable-png */
 
 int
 dmnsn_png_optimize_canvas(dmnsn_canvas *canvas)
 {
-  return 1;
+  errno = ENOTSUP;
+  return -1;
 }
 
 int
 dmnsn_png_write_canvas(const dmnsn_canvas *canvas, FILE *file)
 {
-  return 1;
+  errno = ENOTSUP;
+  return -1;
 }
 
 dmnsn_progress *
 dmnsn_png_write_canvas_async(const dmnsn_canvas *canvas, FILE *file)
 {
+  errno = ENOTSUP;
   return NULL;
 }
 
 dmnsn_canvas *
 dmnsn_png_read_canvas(FILE *file)
 {
+  errno = ENOTSUP;
   return NULL;
 }
 
 dmnsn_progress *
 dmnsn_png_read_canvas_async(dmnsn_canvas **canvas, FILE *file)
 {
+  errno = ENOTSUP;
   return NULL;
 }