diff --git a/helix-term/src/ui/markdown.rs b/helix-term/src/ui/markdown.rs
index ae58d75e8..6bef59d14 100644
--- a/helix-term/src/ui/markdown.rs
+++ b/helix-term/src/ui/markdown.rs
@@ -90,7 +90,13 @@ pub fn highlighted_code_block<'a>(
         if pos == start {
             continue;
         }
-        assert!(pos > start);
+        // The highlighter should always move forward.
+        // If the highlighter malfunctions, bail on syntax highlighting and log an error.
+        debug_assert!(pos > start);
+        if pos < start {
+            log::error!("Failed to highlight '{language}': {text:?}");
+            return styled_multiline_text(text, code_style);
+        }
 
         let style = syntax_highlight_stack
             .iter()