diff --git a/api_test/main.c b/api_test/main.c
index 0df1a7d8d..7e32ee79b 100644
--- a/api_test/main.c
+++ b/api_test/main.c
@@ -804,6 +804,21 @@ static void render_commonmark(test_batch_runner *runner) {
   free(commonmark);
   cmark_node_free(plain_break_doc);
 
+  // An info string containing a backtick forces a tilde fence, which must
+  // be longer than any run of tildes in the code.
+  static const char tilde_fence[] = "~~~~~ a`b\n"
+                                    "~~~\n"
+                                    "<b>x</b>\n"
+                                    "~~~~~\n";
+  cmark_node *tilde_fence_doc =
+      cmark_parse_document(tilde_fence, sizeof(tilde_fence) - 1,
+                           CMARK_OPT_DEFAULT);
+  commonmark = cmark_render_commonmark(tilde_fence_doc, CMARK_OPT_DEFAULT, 0);
+  STR_EQ(runner, commonmark, "~~~~ a`b\n~~~\n<b>x</b>\n~~~~\n",
+         "render tilde fence longer than tildes in code");
+  free(commonmark);
+  cmark_node_free(tilde_fence_doc);
+
   cmark_node_free(text);
   cmark_node_free(doc);
 }
diff --git a/src/commonmark.c b/src/commonmark.c
index 44ee695d2..1b6268f3f 100644
--- a/src/commonmark.c
+++ b/src/commonmark.c
@@ -73,13 +73,13 @@ static inline void outc(cmark_renderer *renderer, cmark_escaping escape,
   }
 }
 
-static int longest_backtick_sequence(const char *code) {
+static int longest_char_sequence(const char *code, char c) {
   int longest = 0;
   int current = 0;
   size_t i = 0;
   size_t code_len = strlen(code);
   while (i <= code_len) {
-    if (code[i] == '`') {
+    if (code[i] == c) {
       current++;
     } else {
       if (current > longest) {
@@ -281,7 +281,7 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     fencechar[0] = strchr(info, '`') == NULL ? '`' : '~';
     code = cmark_node_get_literal(node);
 
-    numticks = longest_backtick_sequence(code) + 1;
+    numticks = longest_char_sequence(code, fencechar[0]) + 1;
     if (numticks < 3) {
       numticks = 3;
     }