diff --git a/src/pngchunk_int.cpp b/src/pngchunk_int.cpp
index 0a7926c6..56dbd42f 100644
--- a/src/pngchunk_int.cpp
+++ b/src/pngchunk_int.cpp
@@ -103,13 +103,13 @@ namespace Exiv2 {
 
     DataBuf PngChunk::keyTXTChunk(const DataBuf& data, bool stripHeader)
     {
-        // From a tEXt, zTXt, or iTXt chunk,
-        // we get the key, it's a null terminated string at the chunk start
+        // From a tEXt, zTXt, or iTXt chunk, we get the keyword which is null terminated.
         const int offset = stripHeader ? 8 : 0;
-        if (data.size() <= offset) throw Error(kerFailedToReadImageData);
+        if (data.size() <= offset)
+          throw Error(kerFailedToReadImageData);
         const byte *key = data.c_data(offset);
 
-        // Find null string at end of key.
+        // Find null chatecter at end of keyword.
         int keysize=0;
         while (key[keysize] != 0)
         {
@@ -117,11 +117,11 @@ namespace Exiv2 {
             // look if keysize is valid.
             if (keysize+offset >= data.size())
                 throw Error(kerFailedToReadImageData);
+            /// \todo move conditional out of the loop
         }
 
         return DataBuf(key, keysize);
-
-    } // PngChunk::keyTXTChunk
+    }
 
     DataBuf PngChunk::parseTXTChunk(const DataBuf& data,
                                     int            keysize,
diff --git a/src/pngimage.cpp b/src/pngimage.cpp
index ccdc624e..45f21ee0 100644
--- a/src/pngimage.cpp
+++ b/src/pngimage.cpp
@@ -712,14 +712,14 @@ namespace Exiv2 {
                     std::cout << "Exiv2::PngImage::doWriteMetadata: strip " << szChunk
                               << " chunk (length: " << dataOffset << ")" << std::endl;
 #endif
-                }
-                else
+                } else
                 {
 #ifdef EXIV2_DEBUG_MESSAGES
                     std::cout << "Exiv2::PngImage::doWriteMetadata: write " << szChunk
                               << " chunk (length: " << dataOffset << ")" << std::endl;
 #endif
-                    if (outIo.write(chunkBuf.c_data(), chunkBuf.size()) != chunkBuf.size()) throw Error(kerImageWriteFailed);
+                    if (outIo.write(chunkBuf.c_data(), chunkBuf.size()) != chunkBuf.size())
+                        throw Error(kerImageWriteFailed);
                 }
             } else {
                 // Write all others chunk as well.
diff --git a/unitTests/CMakeLists.txt b/unitTests/CMakeLists.txt
index f67f6122..1933c922 100644
--- a/unitTests/CMakeLists.txt
+++ b/unitTests/CMakeLists.txt
@@ -12,6 +12,7 @@ add_executable(unit_tests
     test_futils.cpp
     test_helper_functions.cpp
     test_image_int.cpp
+    test_pngimage.cpp
     test_safe_op.cpp
     test_slice.cpp
     test_tiffheader.cpp
diff --git a/unitTests/test_pngimage.cpp b/unitTests/test_pngimage.cpp
new file mode 100644
index 00000000..0474bc31
--- /dev/null
+++ b/unitTests/test_pngimage.cpp
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2004-2022 Exiv2 authors
+ * This program is part of the Exiv2 distribution.
+ *
+ * This program 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 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, 5th Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <exiv2/pngimage.hpp>
+#include "pngchunk_int.hpp" // This is not part of the public API
+
+#include <gtest/gtest.h>
+
+#include <array>
+#include <algorithm>
+
+using namespace Exiv2;
+
+TEST(PngChunk, keyTxtChunkExtractsKeywordCorrectlyInPresenceOfNullChar)
+{
+  // The following data is: '\0\0"AzTXtRaw profile type exif\0\0x'
+  std::array<std::uint8_t, 32> data{0x00, 0x00, 0x22, 0x41, 0x7a, 0x54, 0x58, 0x74,
+                                    0x52, 0x61, 0x77, 0x20, 0x70, 0x72, 0x6f, 0x66,
+                                    0x69, 0x6c, 0x65, 0x20, 0x74, 0x79, 0x70, 0x65,
+                                    0x20, 0x65, 0x78, 0x69, 0x66, 0x00, 0x00, 0x78};
+
+  DataBuf chunkBuf(data.data(), static_cast<long>(data.size()));
+  DataBuf key = Internal::PngChunk::keyTXTChunk(chunkBuf, true);
+  ASSERT_EQ(21, key.size());
+
+  ASSERT_TRUE(std::equal(key.data(), key.data()+key.size(), data.data()+8, data.data()+8+key.size()));
+}
+
+
+TEST(PngChunk, keyTxtChunkThrowsExceptionWhenThereIsNoNullChar)
+{
+  // The following data is: '\0\0"AzTXtRaw profile type exifx'
+  std::array<std::uint8_t, 30> data{0x00, 0x00, 0x22, 0x41, 0x7a, 0x54, 0x58, 0x74,
+                                    0x52, 0x61, 0x77, 0x20, 0x70, 0x72, 0x6f, 0x66,
+                                    0x69, 0x6c, 0x65, 0x20, 0x74, 0x79, 0x70, 0x65,
+                                    0x20, 0x65, 0x78, 0x69, 0x66, 0x78};
+
+  DataBuf chunkBuf(data.data(), static_cast<long>(data.size()));
+  ASSERT_THROW(Internal::PngChunk::keyTXTChunk(chunkBuf, true), Exiv2::Error);
+}