diff --git a/src/reader.c b/src/reader.c
--- a/src/reader.c
+++ b/src/reader.c
@@ -407,6 +407,41 @@
         }
       r->nread += *nread;
     }
+  else if (r->type == READER_TYPE_FD)
+    {
+      ssize_t n;
+
+      if (r->eof)
+        return gpg_error (GPG_ERR_EOF);
+
+      if (!length)
+        {
+          *nread = 0;
+          return 0;
+        }
+
+      n = read (r->u.fd, buffer, length);
+      if (n > 0)
+        {
+          r->nread += n;
+          *nread = n;
+        }
+      else
+        {
+          *nread = 0;
+
+          if (n < 0)
+            {
+              r->error = errno;
+              return gpg_error_from_errno (errno);
+            }
+          else
+            {
+              r->eof = 1;
+              return gpg_error (GPG_ERR_EOF);
+            }
+        }
+    }
   else
     return gpg_error (GPG_ERR_BUG);
 
diff --git a/tests/Makefile.am b/tests/Makefile.am
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -39,7 +39,7 @@
 BUILT_SOURCES = oidtranstbl.h
 CLEANFILES = oidtranstbl.h
 
-TESTS = cert-basic t-crl-parser t-dnparser t-oid
+TESTS = cert-basic t-crl-parser t-dnparser t-oid t-reader
 
 AM_CFLAGS = $(GPG_ERROR_CFLAGS)
 AM_LDFLAGS = -no-install
diff --git a/tests/t-reader.c b/tests/t-reader.c
new file mode 100644
--- /dev/null
+++ b/tests/t-reader.c
@@ -0,0 +1,207 @@
+/* t-reader.c - basic tests for the reader object
+ *      Copyright (C) 2017 g10 Code GmbH
+ *
+ * This file is part of KSBA.
+ *
+ * KSBA is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * KSBA is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <time.h>
+#include <errno.h>
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <gpg-error.h>
+
+#include "../src/ksba.h"
+#include "t-common.h"
+
+void
+test_fd(const char* path)
+{
+  int fd = open (path, O_RDONLY);
+  gpg_error_t err = 0;
+  ksba_reader_t reader;
+  ksba_cert_t cert;
+
+  if (fd < 0)
+    {
+      perror ("open() failed");
+      exit (1);
+    }
+
+  if ((err = ksba_reader_new (&reader)))
+    {
+      fprintf (stderr, "ksba_reader_new() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_reader_set_fd (reader, fd)))
+    {
+      fprintf (stderr, "ksba_reader_set_fd() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_cert_new (&cert)))
+    {
+      fprintf (stderr, "ksba_cert_new() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_cert_read_der (cert, reader)))
+    {
+      fprintf(stderr, "ksba_cert_read_der() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  ksba_cert_release (cert);
+  ksba_reader_release (reader);
+  close (fd);
+}
+
+void
+test_file(const char* path)
+{
+  FILE* fp = fopen (path, "r");
+  gpg_error_t err = 0;
+  ksba_reader_t reader;
+  ksba_cert_t cert;
+
+  if (!fp)
+    {
+      perror ("fopen() failed");
+      exit (1);
+    }
+
+  if ((err = ksba_reader_new (&reader)))
+    {
+      fprintf (stderr, "ksba_reader_new() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_reader_set_file (reader, fp)))
+    {
+      fprintf (stderr, "ksba_reader_set_fd() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_cert_new (&cert)))
+    {
+      fprintf (stderr, "ksba_cert_new() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_cert_read_der (cert, reader)))
+    {
+      fprintf(stderr, "ksba_cert_read_der() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  ksba_cert_release (cert);
+  ksba_reader_release (reader);
+  fclose (fp);
+}
+
+void
+test_mem(const char* path)
+{
+  int fd = open (path, O_RDONLY);
+  gpg_error_t err = 0;
+  ksba_reader_t reader;
+  ksba_cert_t cert;
+  char *mem = NULL;
+  ssize_t ret = 0;
+  size_t p = 0;
+  struct stat st;
+
+  if (fd < 0)
+    {
+      perror ("fopen() failed");
+      exit (1);
+    }
+
+  if (fstat (fd, &st))
+    {
+      fprintf (stderr, "fstat() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  mem = xmalloc(st.st_size);
+
+  while (p < st.st_size && (ret = read(fd, mem + p, st.st_size - p)))
+    {
+      if (ret < 0)
+        {
+          fprintf (stderr, "read() failed: %s\n", gpg_strerror (err));
+          exit (1);
+        }
+      p += ret;
+    }
+
+  if ((err = ksba_reader_new (&reader)))
+    {
+      exit (1);
+    }
+
+  if ((err = ksba_reader_set_mem (reader, mem, st.st_size)))
+    {
+      fprintf (stderr, "ksba_reader_set_mem() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_cert_new (&cert)))
+    {
+      fprintf (stderr, "ksba_cert_new() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  if ((err = ksba_cert_read_der (cert, reader)))
+    {
+      fprintf(stderr, "ksba_cert_read_der() failed: %s\n", gpg_strerror (err));
+      exit (1);
+    }
+
+  ksba_cert_release (cert);
+  ksba_reader_release (reader);
+  xfree (mem);
+  close (fd);
+}
+
+int
+main (int argc, char **argv)
+{
+  if (argc == 1)
+    {
+      test_fd (prepend_srcdir ("cert_g10code_test1.der"));
+      test_file (prepend_srcdir ("cert_g10code_test1.der"));
+      test_mem (prepend_srcdir ("cert_g10code_test1.der"));
+    }
+  else
+    {
+      for (int i = 1; i < argc; ++i)
+        {
+          test_fd (argv[i]);
+          test_file (argv[i]);
+          test_mem (argv[i]);
+        }
+    }
+
+  return 0;
+}