diff --git a/ZRColaCompile/dbsource.cpp b/ZRColaCompile/dbsource.cpp
index a850611..f7cbf71 100644
--- a/ZRColaCompile/dbsource.cpp
+++ b/ZRColaCompile/dbsource.cpp
@@ -262,7 +262,7 @@ bool ZRCola::DBSource::SelectKeySequences(ATL::CComPtr<ADORecordset> &rs) const
     wxCHECK(SUCCEEDED(::CoCreateInstance(CLSID_CADORecordset, NULL, CLSCTX_ALL, IID_IADORecordset, (LPVOID*)&rs)), false);
 
     // Open it.
-    if (FAILED(rs->Open(ATL::CComVariant(L"SELECT [Znak], [tipka] FROM [wrd_KeyCodes]"), ATL::CComVariant(m_db), adOpenStatic, adLockReadOnly, adCmdText))) {
+    if (FAILED(rs->Open(ATL::CComVariant(L"SELECT DISTINCT [Znak], [tipka] FROM [wrd_KeyCodes]"), ATL::CComVariant(m_db), adOpenStatic, adLockReadOnly, adCmdText))) {
         _ftprintf(stderr, wxT("%s: error ZCC0050: Error loading key sequences from database. Please make sure the file is ZRCola.zrc compatible.\n"), m_filename.c_str());
         LogErrors();
         return false;
diff --git a/ZRColaCompile/main.cpp b/ZRColaCompile/main.cpp
index 068f68c..5cce0ee 100644
--- a/ZRColaCompile/main.cpp
+++ b/ZRColaCompile/main.cpp
@@ -464,6 +464,19 @@ int _tmain(int argc, _TCHAR *argv[])
                 qsort_s(db.idxChr.data(), count, sizeof(unsigned __int32), CompareKeySequenceChar, db.data.data());
                 qsort_s(db.idxKey.data(), count, sizeof(unsigned __int32), CompareKeySequenceKey , db.data.data());
 
+                // Check key sequences.
+                for (std::vector<unsigned __int32>::size_type i = 1, n = db.idxKey.size(); i < n; i++) {
+                    const ZRCola::keyseq_db::keyseq
+                        &ks1 = (const ZRCola::keyseq_db::keyseq&)db.data[db.idxKey[i - 1]],
+                        &ks2 = (const ZRCola::keyseq_db::keyseq&)db.data[db.idxKey[i    ]];
+
+                    if (CompareSequence(ks1.seq, ks1.seq_len, ks2.seq, ks2.seq_len) == 0) {
+                        std::wstring seq_str;
+                        ZRCola::keyseq_db::GetSequenceAsText(ks1.seq, ks1.seq_len, seq_str);
+                        _ftprintf(stderr, wxT("%s: warning ZCC0007: Duplicate key sequence (%ls => %04X or %04X). The keyboard behaviour will be unpredictable.\n"), (LPCTSTR)filenameIn.c_str(), seq_str.c_str(), ks1.chr, ks2.chr);
+                    }
+                }
+
                 // Write translations to file.
                 dst << ZRCola::keyseq_rec(db);
             } else {
@@ -479,7 +492,7 @@ int _tmain(int argc, _TCHAR *argv[])
     stdex::idrec::close<ZRCola::recordid_t, ZRCola::recordsize_t, ZRCOLA_RECORD_ALIGN>(dst, dst_start);
 
     if (dst.fail()) {
-        _ftprintf(stderr, wxT("%s: error ZCC0007: Writing to output file failed.\n"), (LPCTSTR)filenameOut.c_str());
+        _ftprintf(stderr, wxT("%s: error ZCC1000: Writing to output file failed.\n"), (LPCTSTR)filenameOut.c_str());
         has_errors = true;
     }
 
diff --git a/lib/libZRColaUI/include/zrcolaui/keyboard.h b/lib/libZRColaUI/include/zrcolaui/keyboard.h
index 13a24f4..7e73891 100644
--- a/lib/libZRColaUI/include/zrcolaui/keyboard.h
+++ b/lib/libZRColaUI/include/zrcolaui/keyboard.h
@@ -63,6 +63,31 @@ namespace ZRCola {
         std::vector<unsigned __int32> idxChr;   ///< Character index
         std::vector<unsigned __int32> idxKey;   ///< Key index
         std::vector<unsigned __int16> data;     ///< Key sequences data
+
+    public:
+        ///
+        /// Get text representation of a given key sequence
+        ///
+        /// \param[in]  seq      Key sequence
+        /// \param[in]  seq_len  Number of elements in \p seq
+        /// \param[out] str     Text representation of a \p seq key sequence
+        ///
+        static void GetSequenceAsText(_In_count_(seq_len) const keyseq::key_t *seq, _In_ size_t seq_len, _Out_ std::wstring& str);
+
+        ///
+        /// Get text representation of a given key sequence
+        ///
+        /// \param[in]  seq      Key sequence
+        /// \param[in]  seq_len  Number of elements in \p seq
+        ///
+        /// \returns Text representation of a \p seq key sequence
+        ///
+        static inline std::wstring GetSequenceAsText(_In_count_(seq_len) const keyseq::key_t *seq, _In_ size_t seq_len)
+        {
+            std::wstring str;
+            GetSequenceAsText(seq, seq_len, str);
+            return str;
+        }
     };
 
 
diff --git a/lib/libZRColaUI/src/keyboard.cpp b/lib/libZRColaUI/src/keyboard.cpp
index ac111f1..b5b41cf 100644
--- a/lib/libZRColaUI/src/keyboard.cpp
+++ b/lib/libZRColaUI/src/keyboard.cpp
@@ -18,3 +18,18 @@
 */
 
 #include "stdafx.h"
+
+
+void ZRCola::keyseq_db::GetSequenceAsText(_In_count_(seq_len) const ZRCola::keyseq_db::keyseq::key_t *seq, _In_ size_t seq_len, _Out_ std::wstring& str)
+{
+    assert(seq || !seq_len);
+
+    str.clear();
+    for (size_t i = 0; i < seq_len; i++) {
+        if (i) str += L", ";
+        if (seq[i].modifiers & keyseq::CTRL ) str += L"Ctrl+";
+        if (seq[i].modifiers & keyseq::ALT  ) str += L"Alt+";
+        if (seq[i].modifiers & keyseq::SHIFT) str += L"Shift+";
+        str += seq[i].key;
+    }
+}
diff --git a/lib/libZRColaUI/src/stdafx.h b/lib/libZRColaUI/src/stdafx.h
index d4f84ec..171035c 100644
--- a/lib/libZRColaUI/src/stdafx.h
+++ b/lib/libZRColaUI/src/stdafx.h
@@ -21,3 +21,5 @@
 
 #include "../../../include/zrcola.h"
 #include "../include/zrcolaui/keyboard.h"
+
+#include <assert.h>
diff --git a/output/data/ZRCola.zrcdb b/output/data/ZRCola.zrcdb
index 14c5484..d39f33a 100644
Binary files a/output/data/ZRCola.zrcdb and b/output/data/ZRCola.zrcdb differ