diff --git a/block.go b/block.go
index 563cb290..1320b6d0 100644
--- a/block.go
+++ b/block.go
@@ -1066,10 +1066,10 @@ func (p *parser) dliPrefix(data []byte) int {
 	i := 0
 
 	// need a : followed by a spaces
-	if data[i] != ':' || data[i+1] != ' ' {
+	if len(data) < 2 || data[i] != ':' || data[i+1] != ' ' {
 		return 0
 	}
-	for data[i] == ' ' {
+	for i < len(data) && data[i] == ' ' {
 		i++
 	}
 	return i + 2
@@ -1126,13 +1126,13 @@ func (p *parser) listItem(out *bytes.Buffer, data []byte, flags *int) int {
 	}
 
 	// skip leading whitespace on first line
-	for data[i] == ' ' {
+	for i < len(data) && data[i] == ' ' {
 		i++
 	}
 
 	// find the end of the line
 	line := i
-	for i > 0 && data[i-1] != '\n' {
+	for i < len(data) && (i == 0 || data[i-1] != '\n') {
 		i++
 	}
 
@@ -1157,9 +1157,13 @@ gatherlines:
 		i++
 
 		// find the end of this line
-		for data[i-1] != '\n' {
+		for i < len(data) && data[i-1] != '\n' {
 			i++
 		}
+		// if we reached end of data without newline, treat as end of line
+		if i > len(data) {
+			i = len(data)
+		}
 		// if it is an empty line, guess that it is part of this item
 		// and move on to the next line
 		if p.isEmpty(data[line:i]) > 0 {
@@ -1246,13 +1250,13 @@ gatherlines:
 			if *flags&LIST_TYPE_DEFINITION != 0 && i < len(data)-1 {
 				// is the next item still a part of this list?
 				next := i
-				for data[next] != '\n' {
+				for next < len(data) && data[next] != '\n' {
 					next++
 				}
 				for next < len(data)-1 && data[next] == '\n' {
 					next++
 				}
-				if i < len(data)-1 && data[i] != ':' && data[next] != ':' {
+				if i < len(data)-1 && data[i] != ':' && next < len(data) && data[next] != ':' {
 					*flags |= LIST_ITEM_END_OF_LIST
 				}
 			} else {
diff --git a/block_test.go b/block_test.go
index f2d998df..e28a4b3c 100644
--- a/block_test.go
+++ b/block_test.go
@@ -1854,3 +1854,72 @@ func TestSanitizedAnchorName(t *testing.T) {
 		}
 	}
 }
+
+// TestListItemBoundsCheck tests that list items without trailing newlines
+// don't cause index out of range panics.
+// See: https://github.com/russross/blackfriday/issues/xxx
+func TestListItemBoundsCheck(t *testing.T) {
+	// These test cases should not panic
+	testCases := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "unordered list without trailing newline",
+			input: "* item",
+		},
+		{
+			name:  "ordered list without trailing newline",
+			input: "1. item",
+		},
+		{
+			name:  "unordered list with spaces no newline",
+			input: "*    item with spaces",
+		},
+		{
+			name:  "ordered list with spaces no newline",
+			input: "1.    item with spaces",
+		},
+		{
+			name:  "nested list without trailing newline",
+			input: "* item\n  * nested",
+		},
+		{
+			name:  "list with multiple items no trailing newline",
+			input: "* item1\n* item2",
+		},
+		{
+			name:  "definition list without trailing newline",
+			input: "Term\n: Definition",
+		},
+		{
+			name:  "empty list marker",
+			input: "* ",
+		},
+		{
+			name:  "list with only spaces after marker",
+			input: "*   ",
+		},
+	}
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("listItem caused panic: %v", r)
+		}
+	}()
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			defer func() {
+				if r := recover(); r != nil {
+					t.Errorf("Test %q panicked: %v", tc.name, r)
+				}
+			}()
+			// Just ensure it doesn't panic - output correctness is secondary
+			_ = runMarkdownBlock(tc.input, 0)
+			_ = runMarkdownBlock(tc.input, EXTENSION_DEFINITION_LISTS)
+			_ = runMarkdownBlock(tc.input, EXTENSION_FENCED_CODE)
+			_ = runMarkdownBlock(tc.input, EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK)
+		})
+	}
+}