--- a/libinterp/parse-tree/lex.ll	Tue Sep 22 19:26:09 2020 +0200
+++ b/libinterp/parse-tree/lex.ll	Tue Sep 22 14:19:11 2020 -0400
@@ -274,7 +274,7 @@
                    || curr_lexer->previous_token_is_binop ()))  \
            {                                                    \
              yyless (0);                                        \
-             unput (',');                                       \
+             curr_lexer->xunput (',');                          \
            }                                                    \
          else                                                   \
            return curr_lexer->handle_number<BASE> ();           \
@@ -295,7 +295,7 @@
                  || curr_lexer->previous_token_is_binop ()))            \
          {                                                              \
            yyless (0);                                                  \
-           unput (',');                                                 \
+           curr_lexer->xunput (',');                                    \
          }                                                              \
        else                                                             \
          {                                                              \
@@ -582,6 +582,10 @@
     curr_lexer->m_filepos.increment_column (yyleng);
   }
 
+%{
+// Whitespace inside matrix lists.
+%}
+
 <MATRIX_START>{S}* {
     curr_lexer->lexer_debug ("<MATRIX_START>{S}*");
 
@@ -607,6 +611,24 @@
   }
 
 %{
+// Continuation lines in matrix constants are handled as whitespace.
+// Allow arbitrary text after the continuation marker.
+%}
+
+<MATRIX_START>\.\.\.{ANY_EXCEPT_NL}*{NL} {
+    curr_lexer->lexer_debug ("<MATRIX_START>\\.\\.\\.{ANY_EXCEPT_NL}*{NL}");
+
+    curr_lexer->handle_continuation ();
+
+    // Even if there wasn't a space before or after the continuation
+    // marker, treat the continuation as if it were.  But since it will
+    // be transformed to a separator later anyway, there's no need to
+    // actually unput a space on the input stream.
+
+    curr_lexer->mark_previous_token_trailing_space ();
+  }
+
+%{
 // For this and the next two rules, we're looking at ']', and we
 // need to know if the next token is '=' or '=='.
 //
@@ -1414,7 +1436,7 @@
                   || curr_lexer->previous_token_is_binop ()))
           {
             yyless (0);
-            unput (',');
+            curr_lexer->xunput (',');
           }
         else
           {