diff --git a/src/Edit.c b/src/Edit.c
index 6565afdde..72ecf7e82 100644
--- a/src/Edit.c
+++ b/src/Edit.c
@@ -692,10 +692,15 @@ BOOL EditLoadFile(
        int* iEncoding,
        int* iEOLMode,
        BOOL *pbUnicodeErr,
-       BOOL *pbFileTooBig)
+       BOOL *pbFileTooBig,
+       BOOL *pbUnkownExt)
 {
-  *pbUnicodeErr = FALSE;
-  *pbFileTooBig = FALSE;
+  if (pbUnicodeErr)
+    *pbUnicodeErr = FALSE;
+  if (pbFileTooBig)
+    *pbFileTooBig = FALSE;
+  if (pbUnkownExt)
+    *pbUnkownExt  = FALSE;
 
   HANDLE hFile = CreateFile(pszFile,
                             GENERIC_READ,
@@ -716,12 +721,26 @@ BOOL EditLoadFile(
   DWORD dwFileSize = GetFileSize(hFile,NULL);
   DWORD dwBufSize = dwFileSize + 16;
 
+  // check for unknown extension
+  LPWSTR lpszExt = PathFindExtension(pszFile);
+  if (!Style_HasLexerForExt(lpszExt)) {
+    if (InfoBox(MBYESNO,L"MsgFileUnknownExt",IDS_WARN_UNKNOWN_EXT,lpszExt) != IDYES) {
+      CloseHandle(hFile);
+      if (pbUnkownExt)
+        *pbUnkownExt = TRUE;
+      Encoding_Source(CPI_NONE);
+      Encoding_SrcWeak(CPI_NONE);
+      return FALSE;
+    }
+  }
+
   // Check if a warning message should be displayed for large files
   DWORD dwFileSizeLimit = IniGetInt(L"Settings2",L"FileLoadWarningMB",1);
   if (dwFileSizeLimit != 0 && dwFileSizeLimit * 1024 * 1024 < dwFileSize) {
-    if (InfoBox(MBYESNO,L"MsgFileSizeWarning",IDS_WARNLOADBIGFILE) != IDYES) {
+    if (InfoBox(MBYESNO,L"MsgFileSizeWarning",IDS_WARN_LOAD_BIG_FILE) != IDYES) {
       CloseHandle(hFile);
-      *pbFileTooBig = TRUE;
+      if (pbFileTooBig)
+        *pbFileTooBig = TRUE;
       Encoding_Source(CPI_NONE);
       Encoding_SrcWeak(CPI_NONE);
       return FALSE;
@@ -734,7 +753,8 @@ BOOL EditLoadFile(
   if (!lpData)
   {
     CloseHandle(hFile);
-    *pbFileTooBig = FALSE;
+    if (pbFileTooBig)
+      *pbFileTooBig = FALSE;
     Encoding_Source(CPI_NONE);
     Encoding_SrcWeak(CPI_NONE);
     return FALSE;
@@ -755,8 +775,7 @@ BOOL EditLoadFile(
   BOOL bPreferOEM = FALSE;
   if (bLoadNFOasOEM)
   {
-    PCWSTR pszExt = pszFile + StringCchLenN(pszFile,MAX_PATH) - 4;
-    if (pszExt >= pszFile && !(StringCchCompareIX(pszExt,L".nfo") && StringCchCompareIX(pszExt,L".diz")))
+    if (lpszExt && !(StringCchCompareIX(lpszExt,L".nfo") && StringCchCompareIX(lpszExt,L".diz")))
       bPreferOEM = TRUE;
   }
 
@@ -822,7 +841,8 @@ BOOL EditLoadFile(
               (bBOM) ? (cbData)/sizeof(WCHAR) : cbData/sizeof(WCHAR) + 1,lpDataUTF8,(int)GlobalSize(lpDataUTF8),NULL,NULL);
 
     if (convCnt == 0) {
-      *pbUnicodeErr = TRUE;
+      if (pbUnicodeErr)
+        *pbUnicodeErr = TRUE;
       convCnt = (DWORD)WideCharToMultiByte(CP_ACP,0,(bBOM) ? (LPWSTR)lpData + 1 : (LPWSTR)lpData,
                 (-1),lpDataUTF8,(int)GlobalSize(lpDataUTF8),NULL,NULL);
     }
diff --git a/src/Edit.h b/src/Edit.h
index 18a1cf405..321b07f6f 100644
--- a/src/Edit.h
+++ b/src/Edit.h
@@ -53,7 +53,7 @@ BOOL  EditIsRecodingNeeded(WCHAR*,int);
 char* EditGetClipboardText(HWND,BOOL,int*,int*);
 BOOL  EditCopyAppend(HWND);
 int   EditDetectEOLMode(HWND,char*,DWORD);
-BOOL  EditLoadFile(HWND,LPCWSTR,BOOL,int*,int*,BOOL*,BOOL*);
+BOOL  EditLoadFile(HWND,LPCWSTR,BOOL,int*,int*,BOOL*,BOOL*,BOOL*);
 BOOL  EditSaveFile(HWND,LPCWSTR,int,BOOL*,BOOL);
 
 void  EditInvertCase(HWND);
diff --git a/src/Notepad3.c b/src/Notepad3.c
index 32a823124..dd0ba9bef 100644
--- a/src/Notepad3.c
+++ b/src/Notepad3.c
@@ -7330,7 +7330,7 @@ int UndoRedoSelectionMap(int token, UndoRedoSelection_t* selection)
 //
 //
 BOOL FileIO(BOOL fLoad,LPCWSTR pszFileName,BOOL bNoEncDetect,int *ienc,int *ieol,
-            BOOL *pbUnicodeErr,BOOL *pbFileTooBig,
+            BOOL *pbUnicodeErr,BOOL *pbFileTooBig, BOOL* pbUnknownExt,
             BOOL *pbCancelDataLoss,BOOL bSaveCopy)
 {
   WCHAR tch[MAX_PATH+40];
@@ -7348,7 +7348,7 @@ BOOL FileIO(BOOL fLoad,LPCWSTR pszFileName,BOOL bNoEncDetect,int *ienc,int *ieol
   UpdateWindow(hwndStatus);
 
   if (fLoad) {
-    fSuccess = EditLoadFile(hwndEdit,pszFileName,bNoEncDetect,ienc,ieol,pbUnicodeErr,pbFileTooBig);
+    fSuccess = EditLoadFile(hwndEdit,pszFileName,bNoEncDetect,ienc,ieol,pbUnicodeErr,pbFileTooBig,pbUnknownExt);
   }
   else {
     int idx;
@@ -7379,9 +7379,10 @@ BOOL FileLoad(BOOL bDontSave,BOOL bNew,BOOL bReload,BOOL bNoEncDetect,LPCWSTR lp
 {
   WCHAR tch[MAX_PATH] = { L'\0' };
   WCHAR szFileName[MAX_PATH] = { L'\0' };
-  BOOL fSuccess;
   BOOL bUnicodeErr = FALSE;
   BOOL bFileTooBig = FALSE;
+  BOOL bUnknownExt = FALSE;
+  BOOL fSuccess;
   int fileEncoding = CPI_ANSI_DEFAULT;
 
   if (!bDontSave)
@@ -7501,7 +7502,7 @@ BOOL FileLoad(BOOL bDontSave,BOOL bNew,BOOL bReload,BOOL bNoEncDetect,LPCWSTR lp
     else
       fileEncoding = Encoding_Current(CPI_GET);
 
-    fSuccess = FileIO(TRUE,szFileName,bNoEncDetect,&fileEncoding,&iEOLMode,&bUnicodeErr,&bFileTooBig,NULL,FALSE);
+    fSuccess = FileIO(TRUE,szFileName,bNoEncDetect,&fileEncoding,&iEOLMode,&bUnicodeErr,&bFileTooBig,&bUnknownExt,NULL,FALSE);
     if (fSuccess)
       Encoding_Current(fileEncoding); // load may change encoding
   }
@@ -7570,7 +7571,7 @@ BOOL FileLoad(BOOL bDontSave,BOOL bNew,BOOL bReload,BOOL bNoEncDetect,LPCWSTR lp
       MsgBox(MBWARN,IDS_ERR_UNICODE);
   }
 
-  else if (!bFileTooBig)
+  else if (!(bFileTooBig || bUnknownExt))
     MsgBox(MBWARN,IDS_ERR_LOADFILE,szFileName);
 
   return(fSuccess);
@@ -7708,7 +7709,7 @@ BOOL FileSave(BOOL bSaveAlways,BOOL bAsk,BOOL bSaveAs,BOOL bSaveCopy)
     if (SaveFileDlg(hwndMain,tchFile,COUNTOF(tchFile),tchInitialDir))
     {
       int fileEncoding = Encoding_Current(CPI_GET);
-      fSuccess = FileIO(FALSE, tchFile, FALSE, &fileEncoding, &iEOLMode, NULL, NULL, &bCancelDataLoss, bSaveCopy);
+      fSuccess = FileIO(FALSE, tchFile, FALSE, &fileEncoding, &iEOLMode, NULL, NULL, NULL, &bCancelDataLoss, bSaveCopy);
       //~if (fSuccess) Encoding_Current(fileEncoding); // save should not change encoding
       if (fSuccess)
       {
@@ -7734,7 +7735,7 @@ BOOL FileSave(BOOL bSaveAlways,BOOL bAsk,BOOL bSaveAs,BOOL bSaveCopy)
   }
   else {
     int fileEncoding = Encoding_Current(CPI_GET);
-    fSuccess = FileIO(FALSE,szCurFile,FALSE,&fileEncoding,&iEOLMode,NULL,NULL,&bCancelDataLoss,FALSE);
+    fSuccess = FileIO(FALSE,szCurFile,FALSE,&fileEncoding,&iEOLMode,NULL,NULL,NULL,&bCancelDataLoss,FALSE);
     //~if (fSuccess) Encoding_Current(fileEncoding); // save should not change encoding
   }
 
@@ -7771,7 +7772,7 @@ BOOL FileSave(BOOL bSaveAlways,BOOL bAsk,BOOL bSaveAs,BOOL bSaveCopy)
         if (GetTempPath(MAX_PATH,lpTempPathBuffer) &&
             GetTempFileName(lpTempPathBuffer,TEXT("NP3"),0,szTempFileName)) {
           int fileEncoding = Encoding_Current(CPI_GET);
-          if (FileIO(FALSE,szTempFileName,FALSE,&fileEncoding,&iEOLMode,NULL,NULL,&bCancelDataLoss,TRUE)) {
+          if (FileIO(FALSE,szTempFileName,FALSE,&fileEncoding,&iEOLMode,NULL,NULL,NULL,&bCancelDataLoss,TRUE)) {
             //~Encoding_Current(fileEncoding); // save should not change encoding
             WCHAR szArguments[2048] = { L'\0' };
             LPWSTR lpCmdLine = GetCommandLine();
diff --git a/src/Notepad3.h b/src/Notepad3.h
index e9f156b2b..08929339d 100644
--- a/src/Notepad3.h
+++ b/src/Notepad3.h
@@ -151,7 +151,7 @@ void RestoreSelectionAction(int,DoAction);
 int  UndoRedoSelectionMap(int,UndoRedoSelection_t*);
 
 
-BOOL FileIO(BOOL,LPCWSTR,BOOL,int*,int*,BOOL*,BOOL*,BOOL*,BOOL);
+BOOL FileIO(BOOL,LPCWSTR,BOOL,int*,int*,BOOL*,BOOL*,BOOL*,BOOL*,BOOL);
 BOOL FileLoad(BOOL,BOOL,BOOL,BOOL,LPCWSTR);
 BOOL FileRevert(LPCWSTR);
 BOOL FileSave(BOOL,BOOL,BOOL,BOOL);
diff --git a/src/Notepad3.rc b/src/Notepad3.rc
index 89a64df5b..197c62e5c 100644
Binary files a/src/Notepad3.rc and b/src/Notepad3.rc differ
diff --git a/src/Styles.c b/src/Styles.c
index 4277de706..ecf79093e 100644
--- a/src/Styles.c
+++ b/src/Styles.c
@@ -3413,10 +3413,9 @@ PEDITLEXER __fastcall Style_SniffShebang(char *pchText)
 //
 //  Style_MatchLexer()
 //
-PEDITLEXER __fastcall Style_MatchLexer(LPCWSTR lpszMatch,BOOL bCheckNames)
-{
+PEDITLEXER __fastcall Style_MatchLexer(LPCWSTR lpszMatch,BOOL bCheckNames) {
   int i;
-  WCHAR  tch[256+16] = { L'\0' };
+  WCHAR  tch[256 + 16] = { L'\0' };
   WCHAR  *p1,*p2;
 
   if (!bCheckNames) {
@@ -3426,7 +3425,7 @@ PEDITLEXER __fastcall Style_MatchLexer(LPCWSTR lpszMatch,BOOL bCheckNames)
       StringCchCopy(tch,COUNTOF(tch),pLexArray[i]->szExtensions);
       p1 = tch;
       while (*p1) {
-        p2 = StrChr(p1, L';');
+        p2 = StrChr(p1,L';');
         if (p2)
           *p2 = L'\0';
         else
@@ -3434,7 +3433,7 @@ PEDITLEXER __fastcall Style_MatchLexer(LPCWSTR lpszMatch,BOOL bCheckNames)
         StrTrim(p1,L" .");
         if (StringCchCompareIX(p1,lpszMatch) == 0)
           return(pLexArray[i]);
-        p1 = p2+1;
+        p1 = p2 + 1;
       }
     }
   }
@@ -3454,6 +3453,17 @@ PEDITLEXER __fastcall Style_MatchLexer(LPCWSTR lpszMatch,BOOL bCheckNames)
 }
 
 
+//=============================================================================
+//
+//  Style_HasLexerForExt()
+//
+BOOL Style_HasLexerForExt(LPCWSTR lpszExt)
+{
+  if (lpszExt && (*lpszExt == L'.')) ++lpszExt;
+  return (lpszExt && Style_MatchLexer(lpszExt,FALSE)) ? TRUE : FALSE;
+}
+
+
 //=============================================================================
 //
 //  Style_SetLexerFromFile()
@@ -3512,8 +3522,7 @@ void Style_SetLexerFromFile(HWND hwnd,LPCWSTR lpszFile)
   if (!bFound && bAutoSelect && /* bAutoSelect == FALSE skips lexer search */
       (lpszFile && StringCchLenN(lpszFile,MAX_PATH) > 0 && *lpszExt)) {
 
-    if (*lpszExt == L'.')
-      lpszExt++;
+    if (*lpszExt == L'.') ++lpszExt;
 
     if (!fNoCGIGuess && (StringCchCompareIX(lpszExt,L"cgi") == 0 || StringCchCompareIX(lpszExt,L"fcgi") == 0)) {
       char tchText[256] = { L'\0' };
diff --git a/src/Styles.h b/src/Styles.h
index e930f1180..f97102956 100644
--- a/src/Styles.h
+++ b/src/Styles.h
@@ -88,6 +88,7 @@ void   Style_SetStyles(HWND,int,LPCWSTR);
 void   Style_SetFontQuality(HWND,LPCWSTR);
 void   Style_GetCurrentLexerName(LPWSTR,int);
 int    Style_GetLexerIconId(PEDITLEXER);
+BOOL   Style_HasLexerForExt(LPCWSTR);
 HTREEITEM Style_AddLexerToTreeView(HWND,PEDITLEXER);
 INT_PTR CALLBACK Styles_ConfigDlgProc(HWND,UINT,WPARAM,LPARAM);
 void   Style_ConfigDlg(HWND);
diff --git a/src/resource.h b/src/resource.h
index f4006b0ec..26c243f63 100644
--- a/src/resource.h
+++ b/src/resource.h
@@ -432,7 +432,7 @@
 #define IDS_ERR_ENCODINGNA              50014
 #define IDS_ERR_UNICODE                 50015
 #define IDS_ERR_UNICODE2                50016
-#define IDS_WARNLOADBIGFILE             50017
+#define IDS_WARN_LOAD_BIG_FILE          50017
 #define IDS_ERR_DROP                    50018
 #define IDS_ASK_SAVE                    50019
 #define IDS_ASK_REVERT                  50020
@@ -457,6 +457,7 @@
 #define IDS_SETTINGSNOTSAVED            50039
 #define IDS_EXPORT_FAIL                 50040
 #define IDS_ERR_ACCESSDENIED            50041
+#define IDS_WARN_UNKNOWN_EXT            50042
 #define IDS_CMDLINEHELP                 60000
 #define IDM_EDIT_INSERT_GUID            60001
 #define IDC_STATIC                      -1