diff --git a/crates/djls-template-ast/src/ast.rs b/crates/djls-template-ast/src/ast.rs
index c0f95a2..c4e13b4 100644
--- a/crates/djls-template-ast/src/ast.rs
+++ b/crates/djls-template-ast/src/ast.rs
@@ -47,14 +47,19 @@ impl LineOffsets {
     pub fn position_to_line_col(&self, position: usize) -> (usize, usize) {
         let position = position as u32;
         let line = match self.0.binary_search(&position) {
-            Ok(_) => self.0.partition_point(|&x| x <= position),
-            Err(i) => i,
+            Ok(exact_line) => exact_line,  // Position is at start of this line
+            Err(0) => 0,  // Before first line start
+            Err(next_line) => next_line - 1,  // We're on the previous line
         };
+
+        // Calculate column as offset from line start
         let col = if line == 0 {
             position as usize
         } else {
-            (position - self.0[line - 1]) as usize
+            (position - self.0[line]) as usize
         };
+
+        // Convert to 1-based line number
         (line + 1, col)
     }
 
@@ -348,7 +353,7 @@ mod tests {
                     eprintln!("Line offsets: {:?}", ast.line_offsets());
                     eprintln!("Span: {:?}", span);
                     let (line, col) = ast.line_offsets().position_to_line_col(span.start as usize);
-                    assert_eq!((line, col), (1, 0), "Content should be on line 1, col 0");
+                    assert_eq!((line, col), (2, 0), "Content should be on line 2, col 0");
 
                     // Check closing tag
                     if let Block::Closing { tag } =
diff --git a/crates/djls-template-ast/src/parser.rs b/crates/djls-template-ast/src/parser.rs
index c228a98..731ac83 100644
--- a/crates/djls-template-ast/src/parser.rs
+++ b/crates/djls-template-ast/src/parser.rs
@@ -23,10 +23,13 @@ impl Parser {
         let mut line_offsets = LineOffsets::new();
 
         // First pass: collect line offsets
+        let mut current_line_start = 0;
         for token in self.tokens.tokens() {
             if let TokenType::Newline = token.token_type() {
                 if let Some(start) = token.start() {
-                    line_offsets.add_line(start + 1);
+                    // Add offset for next line
+                    current_line_start = start + 1;
+                    line_offsets.add_line(current_line_start);
                 }
             }
         }
@@ -157,9 +160,11 @@ impl Parser {
                                     if !found_closing {
                                         // Push the last branch if we didn't find a closing tag
                                         nodes.push(Node::Block(Block::Branch {
-                                            tag: branch_tag,
-                                            nodes: branch_nodes,
+                                            tag: branch_tag.clone(),
+                                            nodes: branch_nodes.clone(),
                                         }));
+                                        // Add error for unclosed tag
+                                        self.errors.push(ParserError::Ast(AstError::UnclosedTag(tag_name.clone())));
                                     }
                                     if found_closing {
                                         break;
@@ -192,6 +197,13 @@ impl Parser {
             }
         };
 
+        // Add error if we didn't find a closing tag for a block
+        if let Block::Block { closing: None, tag: tag_ref, .. } = &block {
+            if let Some(expected_closing) = &spec.closing {
+                self.errors.push(ParserError::Ast(AstError::UnclosedTag(tag_ref.name.clone())));
+            }
+        }
+
         Ok(Node::Block(block))
     }