--- tinycdb/cdb.c
+++ tinycdb/cdb.c
@@ -4,7 +4,9 @@
  * Public domain.
  */
 
-#define _GNU_SOURCE	/* #define this even on Windows */
+#ifndef _GNU_SOURCE
+# define _GNU_SOURCE	/* #define this even on Windows */
+#endif
 
 #ifdef _WIN32		/* by the way, how about win64? */
 # include <io.h>
@@ -130,7 +132,8 @@ static int qmode(char *dbname, const char *key, int num, int flags)
     allocbuf(cdb_datalen(&c));
     if (cdb_read(&c, buf, cdb_datalen(&c), cdb_datapos(&c)) != 0)
       error(errno, "unable to read value");
-    fwrite(buf, 1, cdb_datalen(&c), stdout);
+    if (fwrite(buf, 1, cdb_datalen(&c), stdout) != cdb_datalen(&c))
+      error(errno, "unable to output value");
     if (flags & F_MAP) putchar('\n');
     if (num)
       break;
@@ -316,9 +319,7 @@ addrec(struct cdb_make *cdbmp,
   if (r < 0)
     error(errno, "cdb_make_put");
   else if (r && (flags & F_WARNDUP)) {
-    fprintf(stderr, "%s: key `", progname);
-    fwrite(key, 1, klen, stderr);
-    fputs("' duplicated\n", stderr);
+    fprintf(stderr, "%s: key `%.*s' duplicated\n", progname, klen, key);
     if (flags & F_ERRDUP)
       exit(1);
   }