diff --git a/README.md b/README.md
index c4deb56..d5b6c12 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@
 
 * GNU Make or a build tool that CMake supports.
 * A C99 toolchain (compiler, linker, archiver). We actively test with GCC 5.4, Clang 3.8, IAR8 and Visual Studio 2013. More recent versions should work. Slightly older versions may work.
-* Python 3 to generate the test code.
+* Python 3.6 or later to generate the test code.
 * Perl to run the tests.
 
 ### Make
diff --git a/library/net_sockets.c b/library/net_sockets.c
index bdd82ac..2c2a876 100644
--- a/library/net_sockets.c
+++ b/library/net_sockets.c
@@ -90,6 +90,7 @@
 #include <errno.h>
 
 #define IS_EINTR(ret) ((ret) == EINTR)
+#define SOCKET int
 
 #endif /* ( _WIN32 || _WIN32_WCE ) && !EFIX64 && !EFI32 */
 
@@ -494,13 +495,13 @@
     FD_ZERO(&read_fds);
     if (rw & MBEDTLS_NET_POLL_READ) {
         rw &= ~MBEDTLS_NET_POLL_READ;
-        FD_SET(fd, &read_fds);
+        FD_SET((SOCKET) fd, &read_fds);
     }
 
     FD_ZERO(&write_fds);
     if (rw & MBEDTLS_NET_POLL_WRITE) {
         rw &= ~MBEDTLS_NET_POLL_WRITE;
-        FD_SET(fd, &write_fds);
+        FD_SET((SOCKET) fd, &write_fds);
     }
 
     if (rw != 0) {
@@ -608,7 +609,7 @@
     }
 
     FD_ZERO(&read_fds);
-    FD_SET(fd, &read_fds);
+    FD_SET((SOCKET) fd, &read_fds);
 
     tv.tv_sec  = timeout / 1000;
     tv.tv_usec = (timeout % 1000) * 1000;
diff --git a/programs/fuzz/onefile.c b/programs/fuzz/onefile.c
index 8399735..0d202b1 100644
--- a/programs/fuzz/onefile.c
+++ b/programs/fuzz/onefile.c
@@ -18,34 +18,48 @@
     FILE *fp;
     uint8_t *Data;
     size_t Size;
+    const char *argv0 = argv[0] == NULL ? "PROGRAM_NAME" : argv[0];
 
     if (argc != 2) {
+        fprintf(stderr, "Usage: %s REPRODUCER_FILE\n", argv0);
         return 1;
     }
     //opens the file, get its size, and reads it into a buffer
     fp = fopen(argv[1], "rb");
     if (fp == NULL) {
+        fprintf(stderr, "%s: Error in fopen\n", argv0);
+        perror(argv[1]);
         return 2;
     }
     if (fseek(fp, 0L, SEEK_END) != 0) {
+        fprintf(stderr, "%s: Error in fseek(SEEK_END)\n", argv0);
+        perror(argv[1]);
         fclose(fp);
         return 2;
     }
     Size = ftell(fp);
     if (Size == (size_t) -1) {
+        fprintf(stderr, "%s: Error in ftell\n", argv0);
+        perror(argv[1]);
         fclose(fp);
         return 2;
     }
     if (fseek(fp, 0L, SEEK_SET) != 0) {
+        fprintf(stderr, "%s: Error in fseek(0)\n", argv0);
+        perror(argv[1]);
         fclose(fp);
         return 2;
     }
     Data = malloc(Size);
     if (Data == NULL) {
+        fprintf(stderr, "%s: Could not allocate memory\n", argv0);
+        perror(argv[1]);
         fclose(fp);
         return 2;
     }
     if (fread(Data, Size, 1, fp) != 1) {
+        fprintf(stderr, "%s: Error in fread\n", argv0);
+        perror(argv[1]);
         free(Data);
         fclose(fp);
         return 2;