diff --git a/internal/markdown/convert.go b/internal/markdown/convert.go
index efe6983..c749886 100644
--- a/internal/markdown/convert.go
+++ b/internal/markdown/convert.go
@@ -50,6 +50,9 @@ func init() {
 // Convert converts Markdown source to HTML.
 // plantumlServer is the PlantUML server URL for code block conversion.
 func Convert(source []byte, plantumlServer string) ([]byte, error) {
+	// Normalize CRLF to LF so all preprocessors and the parser see consistent line endings.
+	source = bytes.ReplaceAll(source, []byte("\r\n"), []byte("\n"))
+
 	// Pre-process: expand single-line $$...$$ to multi-line for goldmark-mathjax
 	source = PreprocessMathBlocks(source)
 
diff --git a/internal/markdown/convert_test.go b/internal/markdown/convert_test.go
new file mode 100644
index 0000000..06ebfcb
--- /dev/null
+++ b/internal/markdown/convert_test.go
@@ -0,0 +1,22 @@
+package markdown
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestConvert_CRLFMathBlock(t *testing.T) {
+	// Regression: CRLF line endings must not break $$ math block rendering.
+	input := []byte("$$\r\ny = x^2\r\n$$\r\n")
+	html, err := Convert(input, "")
+	if err != nil {
+		t.Fatalf("Convert returned error: %v", err)
+	}
+	s := string(html)
+	if !strings.Contains(s, `\(y = x^2\)`) && !strings.Contains(s, `y = x^2`) {
+		t.Errorf("math content missing from output:\n%s", s)
+	}
+	if strings.Contains(s, `\(\)`) || strings.Contains(s, `\(\r`) {
+		t.Errorf("CRLF leaked into math output:\n%s", s)
+	}
+}