--- a/src/term.c
+++ b/src/term.c
@@ -5412,6 +5412,8 @@ check_termcode(
 		if (STRNCMP(termcodes[idx].code, tp,
 				     (size_t)(slen > len ? len : slen)) == 0)
 		{
+		    int	    looks_like_mouse_start = FALSE;
+
 		    if (len < slen)		// got a partial sequence
 			return -1;		// need to get more chars
 
@@ -5434,15 +5436,48 @@ check_termcode(
 			    }
 		    }
 
-		    // The mouse termcode "ESC [" is also the prefix of
-		    // "ESC [ I" (focus gained).  Only use it when there is
-		    // no other match.  Do use it when a digit is following to
-		    // avoid waiting for more bytes.
 		    if (slen == 2 && len > 2
 			    && termcodes[idx].code[0] == ESC
-			    && termcodes[idx].code[1] == '['
-			    && !isdigit(tp[2]))
+			    && termcodes[idx].code[1] == '[')
 		    {
+			// The mouse termcode "ESC [" is also the prefix of
+			// "ESC [ I" (focus gained) and other keys.  Check some
+			// more bytes to find out.
+			if (!isdigit(tp[2]))
+			{
+			    // ESC [ without number following: Only use it when
+			    // there is no other match.
+			    looks_like_mouse_start = TRUE;
+			}
+			else if (termcodes[idx].name[0] == KS_DEC_MOUSE)
+			{
+			    char_u  *nr = tp + 2;
+			    int	    count = 0;
+
+			    // If a digit is following it could be a key with
+			    // modifier, e.g., ESC [ 1;2P.  Can be confused
+			    // with DEC_MOUSE, which requires four numbers
+			    // following.  If not then it can't be a DEC_MOUSE
+			    // code.
+			    for (;;)
+			    {
+				++count;
+				(void)getdigits(&nr);
+				if (nr >= tp + len)
+				    return -1;	// partial sequence
+				if (*nr != ';')
+				    break;
+				++nr;
+				if (nr >= tp + len)
+				    return -1;	// partial sequence
+			    }
+			    if (count < 4)
+				continue;	// no match
+			}
+		    }
+		    if (looks_like_mouse_start)
+		    {
+			// Only use it when there is no other match.
 			if (mouse_index_found < 0)
 			    mouse_index_found = idx;
 		    }