diff --git a/src/gui_w48.c b/src/gui_w48.c
index cfbbbc0..42cf91f 100644
--- a/src/gui_w48.c
+++ b/src/gui_w48.c
@@ -486,10 +486,11 @@
 
 /*
  * Convert Unicode character "ch" to bytes in "string[slen]".
+ * When "had_alt" is TRUE the ALT key was included in "ch".
  * Return the length.
  */
     static int
-char_to_string(int ch, char_u *string, int slen)
+char_to_string(int ch, char_u *string, int slen, int had_alt)
 {
     int		len;
     int		i;
@@ -522,8 +523,22 @@
 	 * "enc_codepage" is non-zero use the standard Win32 function,
 	 * otherwise use our own conversion function (e.g., for UTF-8). */
 	if (enc_codepage > 0)
+	{
 	    len = WideCharToMultiByte(enc_codepage, 0, wstring, len,
 						       string, slen, 0, NULL);
+	    /* If we had included the ALT key into the character but now the
+	     * upper bit is no longer set, that probably means the conversion
+	     * failed.  Convert the original character and set the upper bit
+	     * afterwards. */
+	    if (had_alt && len == 1 && ch >= 0x80 && string[0] < 0x80)
+	    {
+		wstring[0] = ch & 0x7f;
+		len = WideCharToMultiByte(enc_codepage, 0, wstring, len,
+						       string, slen, 0, NULL);
+		if (len == 1) /* safety check */
+		    string[0] |= 0x80;
+	    }
+	}
 	else
 	{
 	    len = 1;
@@ -573,7 +588,7 @@
     char_u	string[40];
     int		len = 0;
 
-    len = char_to_string(ch, string, 40);
+    len = char_to_string(ch, string, 40, FALSE);
     if (len == 1 && string[0] == Ctrl_C && ctrl_c_interrupts)
     {
 	trash_input_buf();
@@ -640,7 +655,7 @@
     {
 	/* Although the documentation isn't clear about it, we assume "ch" is
 	 * a Unicode character. */
-	len += char_to_string(ch, string + len, 40 - len);
+	len += char_to_string(ch, string + len, 40 - len, TRUE);
     }
 
     add_to_input_buf(string, len);
@@ -1775,7 +1790,7 @@
 		    int	len;
 
 		    /* Handle "key" as a Unicode character. */
-		    len = char_to_string(key, string, 40);
+		    len = char_to_string(key, string, 40, FALSE);
 		    add_to_input_buf(string, len);
 		}
 		break;
diff --git a/src/os_win32.c b/src/os_win32.c
index 960943c..b0502b2 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -1521,7 +1521,12 @@
 #endif
 		   )
 		{
+#ifdef FEAT_MBYTE
+		    n = (*mb_char2bytes)(typeahead[typeaheadlen] | 0x80,
+						    typeahead + typeaheadlen);
+#else
 		    typeahead[typeaheadlen] |= 0x80;
+#endif
 		    modifiers &= ~MOD_MASK_ALT;
 		}
 
diff --git a/src/version.c b/src/version.c
index 2e300f5..3661a8b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -667,6 +667,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    158,
+/**/
     157,
 /**/
     156,