diff --git a/backend/telepen.c b/backend/telepen.c
index 5e8713bc..2b46e360 100644
--- a/backend/telepen.c
+++ b/backend/telepen.c
@@ -60,7 +60,7 @@ static char *TeleTable[] = {
 INTERNAL int telepen(struct zint_symbol *symbol, unsigned char source[], const size_t src_len) {
     unsigned int i, count, check_digit;
     int error_number;
-    char dest[512]; /*14 + 30 * 14 + 14 + 14 + 1 ~ 512 */
+    char dest[521]; /* 12 (start) + 30 * 16 (max for nuls) + 16 (check digit) + 12 (stop) + 1 = 521 */
 
     error_number = 0;
 
@@ -108,7 +108,7 @@ INTERNAL int telepen_num(struct zint_symbol *symbol, unsigned char source[], con
     unsigned int count, check_digit, glyph;
     int error_number;
     size_t i,temp_length = src_len;
-    char dest[1024]; /* 14 + 60 * 14 + 14 + 14 + 1 ~ 1024 */
+    char dest[521]; /* 12 (start) + 30 * 16 (max for nuls) + 16 (check digit) + 12 (stop) + 1 = 521 */
     unsigned char temp[64];
 
     count = 0;
diff --git a/backend/tests/CMakeLists.txt b/backend/tests/CMakeLists.txt
index e416a171..d96574d0 100644
--- a/backend/tests/CMakeLists.txt
+++ b/backend/tests/CMakeLists.txt
@@ -73,5 +73,6 @@ zint_add_test(qr, test_qr)
 zint_add_test(raster, test_raster)
 zint_add_test(rss, test_rss)
 zint_add_test(sjis, test_sjis)
+zint_add_test(telepen, test_telepen)
 zint_add_test(upcean, test_upcean)
 zint_add_test(vector, test_vector)
diff --git a/backend/tests/test_auspost.c b/backend/tests/test_auspost.c
index 1b9f4008..bd61f34b 100644
--- a/backend/tests/test_auspost.c
+++ b/backend/tests/test_auspost.c
@@ -32,7 +32,7 @@
 #include "testcommon.h"
 
 // #181 Christian Hartlage OSS-Fuzz
-static void test_australia_post_fuzz(void)
+static void test_fuzz(void)
 {
     testStart("");
 
@@ -76,7 +76,7 @@ static void test_australia_post_fuzz(void)
 
 int main()
 {
-    test_australia_post_fuzz();
+    test_fuzz();
 
     testReport();
 
diff --git a/backend/tests/test_telepen.c b/backend/tests/test_telepen.c
new file mode 100644
index 00000000..03bdc5c0
--- /dev/null
+++ b/backend/tests/test_telepen.c
@@ -0,0 +1,85 @@
+/*
+    libzint - the open source barcode library
+    Copyright (C) 2008-2020 Robin Stuart <rstuart114@gmail.com>
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+
+    1. Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright
+       notice, this list of conditions and the following disclaimer in the
+       documentation and/or other materials provided with the distribution.
+    3. Neither the name of the project nor the names of its contributors
+       may be used to endorse or promote products derived from this software
+       without specific prior written permission.
+
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+    ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
+    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+    SUCH DAMAGE.
+ */
+/* vim: set ts=4 sw=4 et : */
+
+#include "testcommon.h"
+
+// #181 Nico Gunkel OSS-Fuzz
+static void test_fuzz(void)
+{
+    testStart("");
+
+    int ret;
+    struct item {
+        int symbology;
+        unsigned char* data;
+        int length;
+        int ret;
+    };
+    // s/\/\*[ 0-9]*\*\//\=printf("\/*%2d*\/", line(".") - line("'<"))
+    struct item data[] = {
+        /* 0*/ { BARCODE_TELEPEN, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 30, 0 },
+        /* 1*/ { BARCODE_TELEPEN, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 31, ZINT_ERROR_TOO_LONG },
+        /* 2*/ { BARCODE_TELEPEN_NUM, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 60, ZINT_ERROR_INVALID_DATA },
+        /* 3*/ { BARCODE_TELEPEN_NUM, "040404040404040404040404040404040404040404040404040404040404", 60, 0 },
+        /* 4*/ { BARCODE_TELEPEN_NUM, "1234567890123456789012345678901234567890123456789012345678901", 61, ZINT_ERROR_TOO_LONG },
+        /* 5*/ { BARCODE_TELEPEN_NUM, "00000000000000000000000000000000000000000000000000000000000X", 60, 0 },
+        /* 6*/ { BARCODE_TELEPEN_NUM, "999999999999999999999999999999999999999999999999999999999999", 60, 0 },
+    };
+    int data_size = sizeof(data) / sizeof(struct item);
+
+    for (int i = 0; i < data_size; i++) {
+
+        struct zint_symbol* symbol = ZBarcode_Create();
+        assert_nonnull(symbol, "Symbol not created\n");
+
+        symbol->symbology = data[i].symbology;
+        int length = data[i].length;
+        if (length == -1) {
+            length = strlen(data[i].data);
+        }
+
+        ret = ZBarcode_Encode(symbol, data[i].data, length);
+        assert_equal(ret, data[i].ret, "i:%d ZBarcode_Encode ret %d != %d (%s)\n", i, ret, data[i].ret, symbol->errtxt);
+
+        ZBarcode_Delete(symbol);
+    }
+
+    testFinish();
+}
+
+int main()
+{
+    test_fuzz();
+
+    testReport();
+
+    return 0;
+}