diff --git a/libretro-common/file/nbio/nbio_stdio.c b/libretro-common/file/nbio/nbio_stdio.c
index 88bf5af78e..8c9c4635be 100644
--- a/libretro-common/file/nbio/nbio_stdio.c
+++ b/libretro-common/file/nbio/nbio_stdio.c
@@ -20,7 +20,7 @@ struct nbio_t
 
 static const char * modes[]={ "rb", "wb", "r+b" };
 
-struct nbio_t* nbio_open(const char * filename, enum nbio_mode_t mode)
+struct nbio_t* nbio_open(const char * filename, unsigned mode)
 {
    struct nbio_t* handle = NULL;
    FILE* f=fopen(filename, modes[mode]);
diff --git a/libretro-common/formats/png/rpng.c b/libretro-common/formats/png/rpng.c
index a2986f90fe..fc6f33e260 100644
--- a/libretro-common/formats/png/rpng.c
+++ b/libretro-common/formats/png/rpng.c
@@ -794,6 +794,10 @@ bool rpng_load_image_argb(const char *path, uint32_t **data,
       unsigned *width, unsigned *height)
 {
    long pos, file_len;
+#ifdef NONBLOCKING_TEST
+   uint8_t *buff_data = NULL;
+   struct nbio_t* nbread = NULL;
+#endif
    uint8_t *inflate_buf = NULL;
    struct idat_buffer idat_buf = {0};
    struct png_ihdr ihdr = {0};
@@ -805,16 +809,20 @@ bool rpng_load_image_argb(const char *path, uint32_t **data,
    bool ret      = true;
    FILE *file;
 #ifdef NONBLOCKING_TEST
-   size_t size = 0;
-   bool looped = false;
-   struct nbio_t* read = nbio_open(path, NBIO_READ);
-   void* ptr           = nbio_get_ptr(read, &size);
-   nbio_begin_read(read);
+   {
+      size_t size = 0;
+      bool looped = false;
+      nbread = nbio_open(path, NBIO_READ);
+      void* ptr           = nbio_get_ptr(nbread, &size);
+      nbio_begin_read(nbread);
 
-   while (!nbio_iterate(read)) looped=true;
-   ptr = nbio_get_ptr(read, &size);
-   (void)ptr;
-   (void)looped;
+      while (!nbio_iterate(nbread)) looped=true;
+      ptr = nbio_get_ptr(nbread, &size);
+      (void)ptr;
+      (void)looped;
+
+      buff_data = (uint8_t*)ptr;
+   }
 #endif
    file = fopen(path, "rb");
 
@@ -828,17 +836,19 @@ bool rpng_load_image_argb(const char *path, uint32_t **data,
       GOTO_END_ERROR();
 
    {
+      unsigned i;
       char header[8];
 
 #ifdef NONBLOCKING_TEST
-      /* TODO/FIXME */
+      for (i = 0; i < 8; i++)
+         header[i] = buff_data[i];
 #else
       if (fread(header, 1, sizeof(header), file) != sizeof(header))
          return false;
+#endif
 
       if (memcmp(header, png_magic, sizeof(png_magic)) != 0)
          return false;
-#endif
    }
 
    /* feof() apparently isn't triggered after a seek (IEND). */
@@ -874,7 +884,7 @@ bool rpng_load_image_argb(const char *path, uint32_t **data,
 
 end:
 #ifdef NONBLOCKING_TEST
-   nbio_free(read);
+   nbio_free(nbread);
 #endif
    if (file)
       fclose(file);
diff --git a/libretro-common/include/file/nbio.h b/libretro-common/include/file/nbio.h
index 522b1e9548..910deaae3d 100644
--- a/libretro-common/include/file/nbio.h
+++ b/libretro-common/include/file/nbio.h
@@ -4,20 +4,16 @@
 #include <stddef.h>
 #include <boolean.h>
 
-enum nbio_mode
-{
-   /* The comments tell which mode in fopen() it corresponds to. */
-   NBIO_READ = 0,/* rb */
-   NBIO_WRITE,   /* wb */
-   NBIO_UPDATE,  /* r+b */
-};
+#define NBIO_READ   0
+#define NBIO_WRITE  1
+#define NBIO_UPDATE 2
 
 struct nbio_t;
 
 /*
  * Creates an nbio structure for performing the given operation on the given file.
  */
-struct nbio_t* nbio_open(const char * filename, enum nbio_mode_t mode);
+struct nbio_t* nbio_open(const char * filename, unsigned mode);
 
 /*
  * Starts reading the given file. When done, it will be available in nbio_get_ptr.
@@ -59,4 +55,4 @@ void nbio_cancel(struct nbio_t* handle);
  */
 void nbio_free(struct nbio_t* handle);
 
-#endif
\ No newline at end of file
+#endif