diff --git a/src/blocks.c b/src/blocks.c
index 3ff6da4d9..8ff339ee4 100644
--- a/src/blocks.c
+++ b/src/blocks.c
@@ -984,7 +984,6 @@ static void open_new_blocks(cmark_parser *parser, cmark_node **container,
   bufsize_t matched = 0;
   int lev = 0;
   bool save_partially_consumed_tab;
-  bool has_content;
   int save_offset;
   int save_column;
 
@@ -1057,17 +1056,15 @@ static void open_new_blocks(cmark_parser *parser, cmark_node **container,
       // text
     } else if (!indented && cont_type == CMARK_NODE_PARAGRAPH &&
                (lev =
-                    scan_setext_heading_line(input, parser->first_nonspace))) {
-      // finalize paragraph, resolving reference links
-      has_content = resolve_reference_link_definitions(parser);
-
-      if (has_content) {
-
-        (*container)->type = (uint16_t)CMARK_NODE_HEADING;
-        (*container)->as.heading.level = lev;
-        (*container)->as.heading.setext = true;
-        S_advance_offset(parser, input, input->len - 1 - parser->offset, false);
-      }
+                    scan_setext_heading_line(input, parser->first_nonspace)) &&
+               resolve_reference_link_definitions(parser)) {
+      // Setext underline only if paragraph content remains after resolving
+      // reference definitions; otherwise fall through so `---` can still
+      // be a thematic break.
+      (*container)->type = (uint16_t)CMARK_NODE_HEADING;
+      (*container)->as.heading.level = lev;
+      (*container)->as.heading.setext = true;
+      S_advance_offset(parser, input, input->len - 1 - parser->offset, false);
     } else if (!indented &&
                !(cont_type == CMARK_NODE_PARAGRAPH && !all_matched) &&
                (parser->thematic_break_kill_pos <= parser->first_nonspace) &&
diff --git a/test/regression.txt b/test/regression.txt
index 2eb818444..1426617ab 100644
--- a/test/regression.txt
+++ b/test/regression.txt
@@ -331,3 +331,21 @@ garbage on the same line must not be treated as a title.
 <p>&quot;The title&quot; garbage
 <a href="/bla">bla</a></p>
 ````````````````````````````````
+
+Issue #619: `---` after a link reference definition is a thematic
+break, not a paragraph.
+```````````````````````````````` example
+[f]:r
+---
+.
+<hr />
+````````````````````````````````
+
+```````````````````````````````` example
+[foo]: /url
+---
+[foo]
+.
+<hr />
+<p><a href="/url">foo</a></p>
+````````````````````````````````